<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:fbba174b-f83b-4bbe-bcad-239c4ab81477,g:cf8e5627-1f2d-4382-9187-b4664a2ea9b9-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.inotivco.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="notv-20240930.xsd#CONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_afec9347-ed0b-44c3-bcd3-57912e2b01ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_StatementTable_afec9347-ed0b-44c3-bcd3-57912e2b01ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_3ee0a48f-4a0a-43f1-8b7e-742626f3a969" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_afec9347-ed0b-44c3-bcd3-57912e2b01ee" xlink:to="loc_srt_ProductOrServiceAxis_3ee0a48f-4a0a-43f1-8b7e-742626f3a969" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_3ee0a48f-4a0a-43f1-8b7e-742626f3a969_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_3ee0a48f-4a0a-43f1-8b7e-742626f3a969" xlink:to="loc_srt_ProductsAndServicesDomain_3ee0a48f-4a0a-43f1-8b7e-742626f3a969_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a6d15a6b-c94d-4b43-bb7e-b9ff6ec9b409" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_3ee0a48f-4a0a-43f1-8b7e-742626f3a969" xlink:to="loc_srt_ProductsAndServicesDomain_a6d15a6b-c94d-4b43-bb7e-b9ff6ec9b409" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_52f1096a-5ba3-45b0-a33f-107e6fcf8592" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a6d15a6b-c94d-4b43-bb7e-b9ff6ec9b409" xlink:to="loc_us-gaap_ServiceMember_52f1096a-5ba3-45b0-a33f-107e6fcf8592" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_2a84b766-69a0-43ff-a097-94fb8e818d05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a6d15a6b-c94d-4b43-bb7e-b9ff6ec9b409" xlink:to="loc_us-gaap_ProductMember_2a84b766-69a0-43ff-a097-94fb8e818d05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d189e00c-f50f-4774-85e5-655dba41c2af" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d189e00c-f50f-4774-85e5-655dba41c2af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_cf492bbe-601e-432a-aee4-5c7d8c3150bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_cf492bbe-601e-432a-aee4-5c7d8c3150bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingExpense_c29b6921-fcc7-4e07-8634-8ce930ffd0a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_SellingExpense_c29b6921-fcc7-4e07-8634-8ce930ffd0a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_482d59e4-ce86-4f10-aca8-aa197e32db1b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_482d59e4-ce86-4f10-aca8-aa197e32db1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_bb5d6b4d-55c6-41fe-8a54-0014d0ab13e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_bb5d6b4d-55c6-41fe-8a54-0014d0ab13e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_b60cc04f-ad61-4aae-8566-c17a7a5a929c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_b60cc04f-ad61-4aae-8566-c17a7a5a929c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_946c8aa0-b00c-48f9-9144-9088c720c368" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_81c13b96-d92b-47c0-a25f-7a506abd7083" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_946c8aa0-b00c-48f9-9144-9088c720c368" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_d2331e87-fd64-47da-b983-8922a48f72a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_OperatingIncomeLoss_d2331e87-fd64-47da-b983-8922a48f72a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_bf38cb80-cc08-4b57-b458-20f7b1528753" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_InterestExpenseNonoperating_bf38cb80-cc08-4b57-b458-20f7b1528753" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_a05284ee-556c-48d8-b862-a6119461dd21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_a05284ee-556c-48d8-b862-a6119461dd21" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_37b2eaab-195c-4de6-a88a-4534674c6847" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_37b2eaab-195c-4de6-a88a-4534674c6847" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_a6f98898-9c82-41e1-a4fb-0a9cc2cd15c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_a6f98898-9c82-41e1-a4fb-0a9cc2cd15c1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_c6326258-3dfc-49b5-918a-1c7471d5b412" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_ProfitLoss_c6326258-3dfc-49b5-918a-1c7471d5b412" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_fb8e63a6-ebf9-4cfe-99c8-4c523f95e66e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_fb8e63a6-ebf9-4cfe-99c8-4c523f95e66e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_fcb8793e-218e-47df-8ffd-b9c2e7f66e9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_NetIncomeLoss_fcb8793e-218e-47df-8ffd-b9c2e7f66e9b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_dfe3b2b2-1fce-4265-b447-f171b0577923" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_EarningsPerShareAbstract_dfe3b2b2-1fce-4265-b447-f171b0577923" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_aaf19f71-cf0f-438d-9ffb-3e53a87a986b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_dfe3b2b2-1fce-4265-b447-f171b0577923" xlink:to="loc_us-gaap_EarningsPerShareBasic_aaf19f71-cf0f-438d-9ffb-3e53a87a986b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_1f859b5a-74f5-475a-b9ed-8026cbac2d65" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_dfe3b2b2-1fce-4265-b447-f171b0577923" xlink:to="loc_us-gaap_EarningsPerShareDiluted_1f859b5a-74f5-475a-b9ed-8026cbac2d65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_f3e927a7-76a9-461e-a614-7652f00c7ac5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3a931c72-739b-4ebd-9aa1-2821b9058e98" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_f3e927a7-76a9-461e-a614-7652f00c7ac5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_409951e5-8113-4757-b540-a094781c6538" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_f3e927a7-76a9-461e-a614-7652f00c7ac5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_409951e5-8113-4757-b540-a094781c6538" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_e5dafe89-69da-4972-a305-60a4d446f056" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_f3e927a7-76a9-461e-a614-7652f00c7ac5" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_e5dafe89-69da-4972-a305-60a4d446f056" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/CONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITY" xlink:type="simple" xlink:href="notv-20240930.xsd#CONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/CONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c4411893-3b67-45b9-a21c-80cdc800e475" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_9d5898ff-06a7-45e8-a62a-21a630936eb0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c4411893-3b67-45b9-a21c-80cdc800e475" xlink:to="loc_us-gaap_StatementTable_9d5898ff-06a7-45e8-a62a-21a630936eb0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_772cc889-d2c2-4e44-a14e-8201077fe784" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9d5898ff-06a7-45e8-a62a-21a630936eb0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_772cc889-d2c2-4e44-a14e-8201077fe784" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_772cc889-d2c2-4e44-a14e-8201077fe784_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_772cc889-d2c2-4e44-a14e-8201077fe784" xlink:to="loc_us-gaap_EquityComponentDomain_772cc889-d2c2-4e44-a14e-8201077fe784_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_772cc889-d2c2-4e44-a14e-8201077fe784" xlink:to="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_d4fccf13-f830-44a1-9148-d3777c0fbb28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:to="loc_us-gaap_CommonStockMember_d4fccf13-f830-44a1-9148-d3777c0fbb28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_fc0fe384-5b78-4bac-a476-af31eef030eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_fc0fe384-5b78-4bac-a476-af31eef030eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_d5d4535e-e860-444e-98f7-376d1e2ebd7d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:to="loc_us-gaap_RetainedEarningsMember_d5d4535e-e860-444e-98f7-376d1e2ebd7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ac4e45e8-3da9-42d4-a21e-2a3766595163" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ac4e45e8-3da9-42d4-a21e-2a3766595163" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_91f42ac4-2ce3-479d-8e9f-fdd1f6631beb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8a751ecb-6c07-472b-96e5-dc6f6a20f079" xlink:to="loc_us-gaap_NoncontrollingInterestMember_91f42ac4-2ce3-479d-8e9f-fdd1f6631beb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c4411893-3b67-45b9-a21c-80cdc800e475" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_78024c0c-b6c9-45d3-8a5e-f0ac4eda7c9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_78024c0c-b6c9-45d3-8a5e-f0ac4eda7c9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_f5dabae1-49b5-4900-a796-5d967b863ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_f5dabae1-49b5-4900-a796-5d967b863ea6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_973878d0-d362-4299-8498-47cef76784ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_NetIncomeLoss_973878d0-d362-4299-8498-47cef76784ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NoncontrollingInterestDecreaseFromBusinessCombination_edd90512-bfbc-43fc-9f59-6227b4579516" xlink:href="notv-20240930.xsd#notv_NoncontrollingInterestDecreaseFromBusinessCombination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_notv_NoncontrollingInterestDecreaseFromBusinessCombination_edd90512-bfbc-43fc-9f59-6227b4579516" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_4717e4f6-af27-402b-adb5-4af7f34ca3bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestDecreaseFromRedemptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_4717e4f6-af27-402b-adb5-4af7f34ca3bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_89a03b55-b0a7-452d-9948-09468390bf6e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_89a03b55-b0a7-452d-9948-09468390bf6e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_51b060e3-e007-4d47-88f5-f824ee5af621" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_51b060e3-e007-4d47-88f5-f824ee5af621" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_334b2efc-b308-4f8b-8323-ed0911d233a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_334b2efc-b308-4f8b-8323-ed0911d233a7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_b6a8be18-06e0-43b7-8081-5a8d624333a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_b6a8be18-06e0-43b7-8081-5a8d624333a2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_66fbbc49-383c-44d7-88a2-b66e0c3527ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_66fbbc49-383c-44d7-88a2-b66e0c3527ba" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_22033ecb-60cc-4322-a2c8-202b2b3e95ce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_22033ecb-60cc-4322-a2c8-202b2b3e95ce" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationGainLossRealizedUponSaleOrLiquidationNetOfTax_69c28c64-04c1-4b2c-9baf-51b424526ab5" xlink:href="notv-20240930.xsd#notv_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationGainLossRealizedUponSaleOrLiquidationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_notv_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationGainLossRealizedUponSaleOrLiquidationNetOfTax_69c28c64-04c1-4b2c-9baf-51b424526ab5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_cd99f127-4261-46bf-95a8-5481455942a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_StockholdersEquityOther_cd99f127-4261-46bf-95a8-5481455942a7" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_ae6892e7-7472-4ac9-aad7-86e40655eeb3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0312319-028c-42c5-a3f6-1ea4b603f480" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_ae6892e7-7472-4ac9-aad7-86e40655eeb3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_a08976aa-f003-46ef-b61d-56be9c87285e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_9e998391-3598-4512-8610-a72b07981585" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DESCRIPTIONOFTHEBUSINESSDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DESCRIPTIONOFTHEBUSINESSDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DESCRIPTIONOFTHEBUSINESSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_f5c2b9ee-53d4-44c8-855b-be23bf52b92d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_93f27f02-a070-462c-bcf7-4f4a7bfb6bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_f5c2b9ee-53d4-44c8-855b-be23bf52b92d" xlink:to="loc_us-gaap_LossContingenciesTable_93f27f02-a070-462c-bcf7-4f4a7bfb6bc1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_35637537-74c4-4800-91f8-c20a09e5199a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_93f27f02-a070-462c-bcf7-4f4a7bfb6bc1" xlink:to="loc_srt_StatementGeographicalAxis_35637537-74c4-4800-91f8-c20a09e5199a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_35637537-74c4-4800-91f8-c20a09e5199a_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_35637537-74c4-4800-91f8-c20a09e5199a" xlink:to="loc_srt_SegmentGeographicalDomain_35637537-74c4-4800-91f8-c20a09e5199a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_66cd24cb-8b37-49ef-a085-fcd3abe4a6db" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_35637537-74c4-4800-91f8-c20a09e5199a" xlink:to="loc_srt_SegmentGeographicalDomain_66cd24cb-8b37-49ef-a085-fcd3abe4a6db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_KH_a261d0a2-1048-4872-be9f-ef8e1ad0ab81" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_KH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_66cd24cb-8b37-49ef-a085-fcd3abe4a6db" xlink:to="loc_country_KH_a261d0a2-1048-4872-be9f-ef8e1ad0ab81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_7a3a63a4-f644-42f7-888e-d2dd1d27b726" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfGovernmentOfficialsIncluded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_f5c2b9ee-53d4-44c8-855b-be23bf52b92d" xlink:to="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_7a3a63a4-f644-42f7-888e-d2dd1d27b726" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfImports_19915908-703b-48a9-993c-b69367ebccc8" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfImports"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_f5c2b9ee-53d4-44c8-855b-be23bf52b92d" xlink:to="loc_notv_LossContingencyNumberOfImports_19915908-703b-48a9-993c-b69367ebccc8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:href="notv-20240930.xsd#notv_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:href="notv-20240930.xsd#notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e56de858-1f3b-40d3-bedb-1f27b4fb1751" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_srt_RangeAxis_e56de858-1f3b-40d3-bedb-1f27b4fb1751" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e56de858-1f3b-40d3-bedb-1f27b4fb1751_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e56de858-1f3b-40d3-bedb-1f27b4fb1751" xlink:to="loc_srt_RangeMember_e56de858-1f3b-40d3-bedb-1f27b4fb1751_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9dfc21bc-ff08-402f-b79f-049b728cc5f2" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e56de858-1f3b-40d3-bedb-1f27b4fb1751" xlink:to="loc_srt_RangeMember_9dfc21bc-ff08-402f-b79f-049b728cc5f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3f724b85-faef-49a6-b773-e0704fd84832" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9dfc21bc-ff08-402f-b79f-049b728cc5f2" xlink:to="loc_srt_MinimumMember_3f724b85-faef-49a6-b773-e0704fd84832" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f785ac77-2a69-43cb-85e5-8810d6bcde41" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9dfc21bc-ff08-402f-b79f-049b728cc5f2" xlink:to="loc_srt_MaximumMember_f785ac77-2a69-43cb-85e5-8810d6bcde41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_0a820ce0-a504-4714-9cbb-8bc07284da94" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_0a820ce0-a504-4714-9cbb-8bc07284da94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0a820ce0-a504-4714-9cbb-8bc07284da94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_0a820ce0-a504-4714-9cbb-8bc07284da94" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0a820ce0-a504-4714-9cbb-8bc07284da94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_51ca3c0f-c9ed-4118-91f8-819700a752c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_0a820ce0-a504-4714-9cbb-8bc07284da94" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_51ca3c0f-c9ed-4118-91f8-819700a752c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsTotalMember_ef836069-73bc-4ef8-9eff-4f75f2b77829" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfGoodsTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_51ca3c0f-c9ed-4118-91f8-819700a752c6" xlink:to="loc_us-gaap_CostOfGoodsTotalMember_ef836069-73bc-4ef8-9eff-4f75f2b77829" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_029d20f0-fd5a-401c-a4b4-dfa267feaccc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_51ca3c0f-c9ed-4118-91f8-819700a752c6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_029d20f0-fd5a-401c-a4b4-dfa267feaccc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_d1bc1277-ab92-4c12-b188-fe643eb2aa4b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_d1bc1277-ab92-4c12-b188-fe643eb2aa4b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_d1bc1277-ab92-4c12-b188-fe643eb2aa4b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d1bc1277-ab92-4c12-b188-fe643eb2aa4b" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_d1bc1277-ab92-4c12-b188-fe643eb2aa4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_64963198-3706-432a-8724-dd7878debed4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d1bc1277-ab92-4c12-b188-fe643eb2aa4b" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_64963198-3706-432a-8724-dd7878debed4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_4cd1ecd7-7fba-483d-a134-843a20c4d4cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_64963198-3706-432a-8724-dd7878debed4" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_4cd1ecd7-7fba-483d-a134-843a20c4d4cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_e922b139-80af-4aa3-b467-6044879b008a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_64963198-3706-432a-8724-dd7878debed4" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_e922b139-80af-4aa3-b467-6044879b008a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_c0969e72-fc87-44fc-b8f7-27debe9a2cb1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_c0969e72-fc87-44fc-b8f7-27debe9a2cb1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c0969e72-fc87-44fc-b8f7-27debe9a2cb1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_c0969e72-fc87-44fc-b8f7-27debe9a2cb1" xlink:to="loc_us-gaap_SegmentDomain_c0969e72-fc87-44fc-b8f7-27debe9a2cb1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c5889a0d-f9c7-4a92-9a95-fd3015eaa427" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_c0969e72-fc87-44fc-b8f7-27debe9a2cb1" xlink:to="loc_us-gaap_SegmentDomain_c5889a0d-f9c7-4a92-9a95-fd3015eaa427" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_e2fa9fd3-fac1-4a5a-9336-c426eea3e022" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c5889a0d-f9c7-4a92-9a95-fd3015eaa427" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_e2fa9fd3-fac1-4a5a-9336-c426eea3e022" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_50cebb22-76df-41b6-821e-32f5066385b5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_srt_MajorCustomersAxis_50cebb22-76df-41b6-821e-32f5066385b5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_50cebb22-76df-41b6-821e-32f5066385b5_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_50cebb22-76df-41b6-821e-32f5066385b5" xlink:to="loc_srt_NameOfMajorCustomerDomain_50cebb22-76df-41b6-821e-32f5066385b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_e638a557-7c5e-430d-8901-e16e57cbac6f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_50cebb22-76df-41b6-821e-32f5066385b5" xlink:to="loc_srt_NameOfMajorCustomerDomain_e638a557-7c5e-430d-8901-e16e57cbac6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_OneCustomerMember_741db7a7-041f-4c5f-a3c5-9bcee6879be2" xlink:href="notv-20240930.xsd#notv_OneCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_e638a557-7c5e-430d-8901-e16e57cbac6f" xlink:to="loc_notv_OneCustomerMember_741db7a7-041f-4c5f-a3c5-9bcee6879be2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_5623826c-af32-4e66-9210-9e9ed208d8aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_5623826c-af32-4e66-9210-9e9ed208d8aa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5623826c-af32-4e66-9210-9e9ed208d8aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5623826c-af32-4e66-9210-9e9ed208d8aa" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5623826c-af32-4e66-9210-9e9ed208d8aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_25b51d41-4f08-429d-a740-65e48e75dccd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5623826c-af32-4e66-9210-9e9ed208d8aa" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_25b51d41-4f08-429d-a740-65e48e75dccd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_00e6ca7a-6def-478a-97c2-796ec84ff0f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_25b51d41-4f08-429d-a740-65e48e75dccd" xlink:to="loc_us-gaap_SubsequentEventMember_00e6ca7a-6def-478a-97c2-796ec84ff0f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d0bbf239-4a79-4e63-b2cc-83bb6624a027" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_5bb35ee0-9f62-4e89-ae08-1df10bd5cf45" xlink:to="loc_us-gaap_CreditFacilityAxis_d0bbf239-4a79-4e63-b2cc-83bb6624a027" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d0bbf239-4a79-4e63-b2cc-83bb6624a027_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d0bbf239-4a79-4e63-b2cc-83bb6624a027" xlink:to="loc_us-gaap_CreditFacilityDomain_d0bbf239-4a79-4e63-b2cc-83bb6624a027_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d6522cab-ae9f-4e1f-9462-f73255287e29" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d0bbf239-4a79-4e63-b2cc-83bb6624a027" xlink:to="loc_us-gaap_CreditFacilityDomain_d6522cab-ae9f-4e1f-9462-f73255287e29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AmendedAndRestatedCreditAgreementMember_b168581b-9029-4caf-af25-e103ca7c1612" xlink:href="notv-20240930.xsd#notv_AmendedAndRestatedCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_d6522cab-ae9f-4e1f-9462-f73255287e29" xlink:to="loc_notv_AmendedAndRestatedCreditAgreementMember_b168581b-9029-4caf-af25-e103ca7c1612" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_d72befab-5c69-40f1-8ec8-7311425a5190" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_d6522cab-ae9f-4e1f-9462-f73255287e29" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_d72befab-5c69-40f1-8ec8-7311425a5190" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionGainsAndLossesOnForeignInvestments_02319762-a8ca-4d15-89d8-572d3313193a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConversionGainsAndLossesOnForeignInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_ConversionGainsAndLossesOnForeignInvestments_02319762-a8ca-4d15-89d8-572d3313193a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_a1daf338-c931-42fa-8231-378c6eae9927" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_NumberOfReportableSegments_a1daf338-c931-42fa-8231-378c6eae9927" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NumberOfRevenueStreams_b7aa4c42-0836-4ad5-be48-e63446fc7880" xlink:href="notv-20240930.xsd#notv_NumberOfRevenueStreams"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_NumberOfRevenueStreams_b7aa4c42-0836-4ad5-be48-e63446fc7880" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_PeriodOfWrittenNoticeForTerminationOfFeeForServiceContracts_f4a4b446-ffab-4f3e-afe3-f5d58dc9dad7" xlink:href="notv-20240930.xsd#notv_PeriodOfWrittenNoticeForTerminationOfFeeForServiceContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_PeriodOfWrittenNoticeForTerminationOfFeeForServiceContracts_f4a4b446-ffab-4f3e-afe3-f5d58dc9dad7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_00172d39-7746-41b1-a4b5-7dd659a77963" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_00172d39-7746-41b1-a4b5-7dd659a77963" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_80150a70-403c-4a71-b283-f45b997183ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_80150a70-403c-4a71-b283-f45b997183ad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeFinanceLeaseRenewalTerm1_dd1880b7-d30a-4fea-a91d-9103b84426a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeFinanceLeaseRenewalTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_LesseeFinanceLeaseRenewalTerm1_dd1880b7-d30a-4fea-a91d-9103b84426a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_cc7c7c5e-77e4-45e5-ae9d-6336aef37609" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_cc7c7c5e-77e4-45e5-ae9d-6336aef37609" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_69ef2db8-3f78-4c37-ab38-0cbeda06a464" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_LineOfCredit_69ef2db8-3f78-4c37-ab38-0cbeda06a464" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantCapOnFundsReinvestment_e6c2ae7d-6d72-486b-a458-03bfbe90089b" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantCapOnFundsReinvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_DebtInstrumentCovenantCapOnFundsReinvestment_e6c2ae7d-6d72-486b-a458-03bfbe90089b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_49e189e0-e704-4afd-aa31-606a664d77df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_49e189e0-e704-4afd-aa31-606a664d77df" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalQuarterEnd_ef55b7c0-27a3-4f79-b4e6-08821475df38" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalQuarterEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalQuarterEnd_ef55b7c0-27a3-4f79-b4e6-08821475df38" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalYearEnd_a0d9fb1e-928e-4da3-bf8c-87dae0881d30" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalYearEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_d6b9277e-0b48-4809-aa89-16d333a6420e" xlink:to="loc_notv_DebtInstrumentCovenantGracePeriodSubsequentToAnyFiscalYearEnd_a0d9fb1e-928e-4da3-bf8c-87dae0881d30" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPropertyPlantandEquipmentEstimatedUsefulLivesDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPropertyPlantandEquipmentEstimatedUsefulLivesDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPropertyPlantandEquipmentEstimatedUsefulLivesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_eb17256e-d512-4bb5-9c39-90fc6ebae355" xlink:href="notv-20240930.xsd#notv_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_d7fd9723-f338-4578-b576-b6eb00a1be2e" xlink:href="notv-20240930.xsd#notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_eb17256e-d512-4bb5-9c39-90fc6ebae355" xlink:to="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_d7fd9723-f338-4578-b576-b6eb00a1be2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_9f998fff-0a6a-4566-af61-071be9fe06aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_d7fd9723-f338-4578-b576-b6eb00a1be2e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_9f998fff-0a6a-4566-af61-071be9fe06aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_9f998fff-0a6a-4566-af61-071be9fe06aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_9f998fff-0a6a-4566-af61-071be9fe06aa" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_9f998fff-0a6a-4566-af61-071be9fe06aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_9f998fff-0a6a-4566-af61-071be9fe06aa" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandImprovementsMember_ca12d870-4b76-4396-aad7-a4749a39cf81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_LandImprovementsMember_ca12d870-4b76-4396-aad7-a4749a39cf81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_f8af24c8-266c-4b7d-913d-8112ffa9291e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_f8af24c8-266c-4b7d-913d-8112ffa9291e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_cea1533c-a537-4636-8cf1-66fe61714647" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_cea1533c-a537-4636-8cf1-66fe61714647" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_97ba356b-af92-4196-b318-5b5a529e7b20" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_97ba356b-af92-4196-b318-5b5a529e7b20" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_c70ee02e-5d64-4c40-9987-3f6cb4c9fb60" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_ComputerEquipmentMember_c70ee02e-5d64-4c40-9987-3f6cb4c9fb60" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_44a94ad7-a412-4ab1-8256-61e0e926ce0a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VehiclesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c5cd44fe-dc3e-4707-9c9d-b6197454e513" xlink:to="loc_us-gaap_VehiclesMember_44a94ad7-a412-4ab1-8256-61e0e926ce0a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_63ab25bd-3c48-4878-9b4d-1fcce1536bd8" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_d7fd9723-f338-4578-b576-b6eb00a1be2e" xlink:to="loc_srt_RangeAxis_63ab25bd-3c48-4878-9b4d-1fcce1536bd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_63ab25bd-3c48-4878-9b4d-1fcce1536bd8_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_63ab25bd-3c48-4878-9b4d-1fcce1536bd8" xlink:to="loc_srt_RangeMember_63ab25bd-3c48-4878-9b4d-1fcce1536bd8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_632366fa-6983-494b-a148-e53f5696015e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_63ab25bd-3c48-4878-9b4d-1fcce1536bd8" xlink:to="loc_srt_RangeMember_632366fa-6983-494b-a148-e53f5696015e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_dd36b081-099c-4b76-a2bb-3f31106c96a4" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_632366fa-6983-494b-a148-e53f5696015e" xlink:to="loc_srt_MinimumMember_dd36b081-099c-4b76-a2bb-3f31106c96a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_47c7f01c-c4aa-4d63-ab3c-7139acc12758" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_632366fa-6983-494b-a148-e53f5696015e" xlink:to="loc_srt_MaximumMember_47c7f01c-c4aa-4d63-ab3c-7139acc12758" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_0bcc0184-9e5b-456c-946d-320d3592ae9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_eb17256e-d512-4bb5-9c39-90fc6ebae355" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_0bcc0184-9e5b-456c-946d-320d3592ae9b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESIntangibleAssetsEstimatedUsefulLivesDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESIntangibleAssetsEstimatedUsefulLivesDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/BASISOFPRESENTATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESIntangibleAssetsEstimatedUsefulLivesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_f7779982-f5db-4eab-8741-749440816e59" xlink:href="notv-20240930.xsd#notv_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_e8b8da83-c118-47f0-86aa-1223dcbb3bbc" xlink:href="notv-20240930.xsd#notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_f7779982-f5db-4eab-8741-749440816e59" xlink:to="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_e8b8da83-c118-47f0-86aa-1223dcbb3bbc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_e8b8da83-c118-47f0-86aa-1223dcbb3bbc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_cd068547-51ac-4c4a-9a5c-f78b1e5318eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f7c29d16-4046-4ef4-b240-ad9e8a8d79ca" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_cd068547-51ac-4c4a-9a5c-f78b1e5318eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_9141addd-9c83-4ca6-bc29-a4ca878be95d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_cd068547-51ac-4c4a-9a5c-f78b1e5318eb" xlink:to="loc_us-gaap_CustomerRelationshipsMember_9141addd-9c83-4ca6-bc29-a4ca878be95d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_d336515e-763d-4e8c-8cd4-d2af8a62eaa5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_cd068547-51ac-4c4a-9a5c-f78b1e5318eb" xlink:to="loc_us-gaap_IntellectualPropertyMember_d336515e-763d-4e8c-8cd4-d2af8a62eaa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_bc50889f-0d7f-4c52-a80c-44788d8dccfd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_cd068547-51ac-4c4a-9a5c-f78b1e5318eb" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_bc50889f-0d7f-4c52-a80c-44788d8dccfd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_756503c2-f36b-4dba-a80a-4cec4a536575" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_notv_ScheduleOfSummaryOfSignificantAccountingPoliciesTable_e8b8da83-c118-47f0-86aa-1223dcbb3bbc" xlink:to="loc_srt_RangeAxis_756503c2-f36b-4dba-a80a-4cec4a536575" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_756503c2-f36b-4dba-a80a-4cec4a536575_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_756503c2-f36b-4dba-a80a-4cec4a536575" xlink:to="loc_srt_RangeMember_756503c2-f36b-4dba-a80a-4cec4a536575_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7423fc7a-30d2-4bcb-9126-a6c763c4573d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_756503c2-f36b-4dba-a80a-4cec4a536575" xlink:to="loc_srt_RangeMember_7423fc7a-30d2-4bcb-9126-a6c763c4573d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_463298df-2e50-45dc-80be-1217ea48ec4e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7423fc7a-30d2-4bcb-9126-a6c763c4573d" xlink:to="loc_srt_MinimumMember_463298df-2e50-45dc-80be-1217ea48ec4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_37832c4e-4986-42bf-9db8-e339b0636939" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_7423fc7a-30d2-4bcb-9126-a6c763c4573d" xlink:to="loc_srt_MaximumMember_37832c4e-4986-42bf-9db8-e339b0636939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_4e755699-4244-4ea2-a35e-60d9fc899b03" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_SummaryOfSignificantAccountingPoliciesLineItems_f7779982-f5db-4eab-8741-749440816e59" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_4e755699-4244-4ea2-a35e-60d9fc899b03" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/BUSINESSCOMBINATIONSNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#BUSINESSCOMBINATIONSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/BUSINESSCOMBINATIONSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_19dd1b35-9f34-4ecf-8ca2-aa8767059521" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_19dd1b35-9f34-4ecf-8ca2-aa8767059521" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_412ea3fe-6b6c-4da8-8667-cdd8227c0aca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_19dd1b35-9f34-4ecf-8ca2-aa8767059521" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_412ea3fe-6b6c-4da8-8667-cdd8227c0aca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_412ea3fe-6b6c-4da8-8667-cdd8227c0aca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_412ea3fe-6b6c-4da8-8667-cdd8227c0aca" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_412ea3fe-6b6c-4da8-8667-cdd8227c0aca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f90739cf-67a1-4a9a-944d-bfb7210dbd8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_412ea3fe-6b6c-4da8-8667-cdd8227c0aca" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f90739cf-67a1-4a9a-944d-bfb7210dbd8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_HistionLlcAcquisitionMember_8d6525fe-2308-4593-84a9-5542a6fe9a4c" xlink:href="notv-20240930.xsd#notv_HistionLlcAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f90739cf-67a1-4a9a-944d-bfb7210dbd8c" xlink:to="loc_notv_HistionLlcAcquisitionMember_8d6525fe-2308-4593-84a9-5542a6fe9a4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ProtypiaInc.Member_330fddcf-e902-4880-a423-d2ed56109e31" xlink:href="notv-20240930.xsd#notv_ProtypiaInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f90739cf-67a1-4a9a-944d-bfb7210dbd8c" xlink:to="loc_notv_ProtypiaInc.Member_330fddcf-e902-4880-a423-d2ed56109e31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_724e2681-ab68-4d38-be45-d67e48be807f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_19dd1b35-9f34-4ecf-8ca2-aa8767059521" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_724e2681-ab68-4d38-be45-d67e48be807f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_724e2681-ab68-4d38-be45-d67e48be807f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_724e2681-ab68-4d38-be45-d67e48be807f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_724e2681-ab68-4d38-be45-d67e48be807f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c7661898-42ab-4a44-89e2-6f60adb0616a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_724e2681-ab68-4d38-be45-d67e48be807f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c7661898-42ab-4a44-89e2-6f60adb0616a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_8ded40dd-baaa-4a6e-9068-027dc2807e86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c7661898-42ab-4a44-89e2-6f60adb0616a" xlink:to="loc_us-gaap_CustomerRelationshipsMember_8ded40dd-baaa-4a6e-9068-027dc2807e86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_6c013623-15a1-4498-a3b7-28b3625d3963" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c7661898-42ab-4a44-89e2-6f60adb0616a" xlink:to="loc_us-gaap_IntellectualPropertyMember_6c013623-15a1-4498-a3b7-28b3625d3963" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_eda902c2-f44c-4117-be6b-0df9a5ef656b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_eda902c2-f44c-4117-be6b-0df9a5ef656b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_edee1274-76fd-479a-b097-9695325152ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_edee1274-76fd-479a-b097-9695325152ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_b4914547-2a86-4c4a-8a1a-dad017475534" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned_b4914547-2a86-4c4a-8a1a-dad017475534" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_709809dd-436f-4ee1-884d-8b0d4aceed3b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_709809dd-436f-4ee1-884d-8b0d4aceed3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_3c7ae50a-f5db-4056-ad4a-1f5b3dc01e21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_74fc78ee-b0ea-455f-9418-7c9e743c79d9" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_3c7ae50a-f5db-4056-ad4a-1f5b3dc01e21" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/BUSINESSCOMBINATIONSFinaldeterminationoffairvalueofassetsacquiredandliabilitiesassumedDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#BUSINESSCOMBINATIONSFinaldeterminationoffairvalueofassetsacquiredandliabilitiesassumedDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/BUSINESSCOMBINATIONSFinaldeterminationoffairvalueofassetsacquiredandliabilitiesassumedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_65f53e00-5eb1-4e23-b1bc-b717b8b4a24c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb044a4f-e6d5-43f5-a394-b769e7609073" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_65f53e00-5eb1-4e23-b1bc-b717b8b4a24c" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb044a4f-e6d5-43f5-a394-b769e7609073" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_8cbcffd6-a40c-4686-b137-1fe8b925bcb5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb044a4f-e6d5-43f5-a394-b769e7609073" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_8cbcffd6-a40c-4686-b137-1fe8b925bcb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8cbcffd6-a40c-4686-b137-1fe8b925bcb5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8cbcffd6-a40c-4686-b137-1fe8b925bcb5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8cbcffd6-a40c-4686-b137-1fe8b925bcb5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_661a88d2-f5d8-4a97-b450-7754a10c701b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8cbcffd6-a40c-4686-b137-1fe8b925bcb5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_661a88d2-f5d8-4a97-b450-7754a10c701b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ProtypiaInc.Member_83c44858-7e82-42f8-b12f-05705f30097d" xlink:href="notv-20240930.xsd#notv_ProtypiaInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_661a88d2-f5d8-4a97-b450-7754a10c701b" xlink:to="loc_notv_ProtypiaInc.Member_83c44858-7e82-42f8-b12f-05705f30097d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_65f53e00-5eb1-4e23-b1bc-b717b8b4a24c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_64415243-8001-4a8d-b4e0-eecc4011af80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:to="loc_us-gaap_Goodwill_64415243-8001-4a8d-b4e0-eecc4011af80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6d77f00c-c332-46ea-836b-8f4601b9068d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6d77f00c-c332-46ea-836b-8f4601b9068d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_e6ef27dd-54ea-4f75-866b-52c06ded2cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_e6ef27dd-54ea-4f75-866b-52c06ded2cdb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_3c1b78b2-6f6a-414c-a64d-26c0b52156ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_3c1b78b2-6f6a-414c-a64d-26c0b52156ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_301f79a9-80d9-42ce-830f-712a6a921afd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_dec492bb-0c43-4bca-a5be-6df1210f7e8f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_301f79a9-80d9-42ce-830f-712a6a921afd" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8ed66d27-fc9c-473d-852e-cb76f8f637ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8ed66d27-fc9c-473d-852e-cb76f8f637ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_656dfac9-4b06-4696-a27e-8a17810a5e46" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8ed66d27-fc9c-473d-852e-cb76f8f637ec" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_656dfac9-4b06-4696-a27e-8a17810a5e46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent_9a5f3502-2a50-4d9c-bdc7-0e3deaaa2e34" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent_9a5f3502-2a50-4d9c-bdc7-0e3deaaa2e34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_8bd0c521-d9d6-4b1a-87ce-6abbcab1a732" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetGrossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_8bd0c521-d9d6-4b1a-87ce-6abbcab1a732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRefundLiabilityCurrent_0719dfc7-fb87-45be-b02b-93a38f39f914" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRefundLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_CustomerRefundLiabilityCurrent_0719dfc7-fb87-45be-b02b-93a38f39f914" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_76448c9a-299f-4c1e-bb21-e4ed80258835" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_76448c9a-299f-4c1e-bb21-e4ed80258835" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AllowanceForDoubtfulUncollectedArchiveInvoices_bfe111c2-a2f6-4e0a-80b1-22db88f46d0c" xlink:href="notv-20240930.xsd#notv_AllowanceForDoubtfulUncollectedArchiveInvoices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_AllowanceForDoubtfulUncollectedArchiveInvoices_bfe111c2-a2f6-4e0a-80b1-22db88f46d0c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_34a697cb-e7f6-4617-af09-f7d9bba8f1e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_34a697cb-e7f6-4617-af09-f7d9bba8f1e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6d4e2e83-bf32-4820-8db3-3494f0c27173" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6d4e2e83-bf32-4820-8db3-3494f0c27173" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1_e63514a4-c8ef-4c1e-94bd-2f254cd7f6e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1_e63514a4-c8ef-4c1e-94bd-2f254cd7f6e6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_PercentageOfUnbilledRevenueBilled_4b435236-8862-409a-b0a6-58eb8043bf80" xlink:href="notv-20240930.xsd#notv_PercentageOfUnbilledRevenueBilled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_PercentageOfUnbilledRevenueBilled_4b435236-8862-409a-b0a6-58eb8043bf80" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage_616cb944-a3af-4706-b292-0d8614c2b636" xlink:href="notv-20240930.xsd#notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage_616cb944-a3af-4706-b292-0d8614c2b636" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails_1" xlink:type="simple" xlink:href="notv-20240930.xsd#REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails_1"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/REVENUEFROMCONTRACTSWITHCLIENTSContractAssetsandContractLiabilitiesDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8ed66d27-fc9c-473d-852e-cb76f8f637ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_8ed66d27-fc9c-473d-852e-cb76f8f637ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent_9a5f3502-2a50-4d9c-bdc7-0e3deaaa2e34" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerReceivableBeforeAllowanceForCreditLossCurrent_9a5f3502-2a50-4d9c-bdc7-0e3deaaa2e34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_8bd0c521-d9d6-4b1a-87ce-6abbcab1a732" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetGrossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_8bd0c521-d9d6-4b1a-87ce-6abbcab1a732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRefundLiabilityCurrent_0719dfc7-fb87-45be-b02b-93a38f39f914" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRefundLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_CustomerRefundLiabilityCurrent_0719dfc7-fb87-45be-b02b-93a38f39f914" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_76448c9a-299f-4c1e-bb21-e4ed80258835" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_76448c9a-299f-4c1e-bb21-e4ed80258835" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AllowanceForDoubtfulUncollectedArchiveInvoices_bfe111c2-a2f6-4e0a-80b1-22db88f46d0c" xlink:href="notv-20240930.xsd#notv_AllowanceForDoubtfulUncollectedArchiveInvoices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_AllowanceForDoubtfulUncollectedArchiveInvoices_bfe111c2-a2f6-4e0a-80b1-22db88f46d0c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_34a697cb-e7f6-4617-af09-f7d9bba8f1e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_34a697cb-e7f6-4617-af09-f7d9bba8f1e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6d4e2e83-bf32-4820-8db3-3494f0c27173" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6d4e2e83-bf32-4820-8db3-3494f0c27173" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1_e63514a4-c8ef-4c1e-94bd-2f254cd7f6e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionYear1_e63514a4-c8ef-4c1e-94bd-2f254cd7f6e6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_PercentageOfUnbilledRevenueBilled_4b435236-8862-409a-b0a6-58eb8043bf80" xlink:href="notv-20240930.xsd#notv_PercentageOfUnbilledRevenueBilled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_PercentageOfUnbilledRevenueBilled_4b435236-8862-409a-b0a6-58eb8043bf80" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage_616cb944-a3af-4706-b292-0d8614c2b636" xlink:href="notv-20240930.xsd#notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_45c4a263-3aab-4dc7-bd0f-5b89e60b6454" xlink:to="loc_notv_ContractWithCustomerLiabilityRevenueRecognizedPercentage_616cb944-a3af-4706-b292-0d8614c2b636" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#SEGMENTANDGEOGRAPHICINFORMATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_cb39708e-1672-434a-b53e-9eb885ba1728" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_cb39708e-1672-434a-b53e-9eb885ba1728" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_5647778e-9f1f-490a-96a8-09e87f953cd9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_cb39708e-1672-434a-b53e-9eb885ba1728" xlink:to="loc_srt_ConsolidationItemsAxis_5647778e-9f1f-490a-96a8-09e87f953cd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_5647778e-9f1f-490a-96a8-09e87f953cd9_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_5647778e-9f1f-490a-96a8-09e87f953cd9" xlink:to="loc_srt_ConsolidationItemsDomain_5647778e-9f1f-490a-96a8-09e87f953cd9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c553a1c9-d851-4f09-8c5d-b90517aa0edf" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_5647778e-9f1f-490a-96a8-09e87f953cd9" xlink:to="loc_srt_ConsolidationItemsDomain_c553a1c9-d851-4f09-8c5d-b90517aa0edf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_648314e4-38a0-47e8-a397-84746e1b6ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c553a1c9-d851-4f09-8c5d-b90517aa0edf" xlink:to="loc_us-gaap_IntersegmentEliminationMember_648314e4-38a0-47e8-a397-84746e1b6ab2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_5e469ad9-d306-4c37-9ba6-83cf6b4b4ba6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c553a1c9-d851-4f09-8c5d-b90517aa0edf" xlink:to="loc_us-gaap_CorporateNonSegmentMember_5e469ad9-d306-4c37-9ba6-83cf6b4b4ba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_8244e09e-fded-4d79-91ee-45402b5896f9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_cb39708e-1672-434a-b53e-9eb885ba1728" xlink:to="loc_srt_ProductOrServiceAxis_8244e09e-fded-4d79-91ee-45402b5896f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8244e09e-fded-4d79-91ee-45402b5896f9_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_8244e09e-fded-4d79-91ee-45402b5896f9" xlink:to="loc_srt_ProductsAndServicesDomain_8244e09e-fded-4d79-91ee-45402b5896f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_1a69f8ea-e8f1-42e1-871f-e0583bbf7154" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_8244e09e-fded-4d79-91ee-45402b5896f9" xlink:to="loc_srt_ProductsAndServicesDomain_1a69f8ea-e8f1-42e1-871f-e0583bbf7154" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_054c8c47-cd4d-4d70-9ed8-910f5a73589b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1a69f8ea-e8f1-42e1-871f-e0583bbf7154" xlink:to="loc_us-gaap_ProductMember_054c8c47-cd4d-4d70-9ed8-910f5a73589b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_cddcf6f8-1793-452b-9cc9-6d206a21333e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_cb39708e-1672-434a-b53e-9eb885ba1728" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_cddcf6f8-1793-452b-9cc9-6d206a21333e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cddcf6f8-1793-452b-9cc9-6d206a21333e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cddcf6f8-1793-452b-9cc9-6d206a21333e" xlink:to="loc_us-gaap_SegmentDomain_cddcf6f8-1793-452b-9cc9-6d206a21333e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_7bca06c7-020c-4e56-8a95-90e1fc6a7931" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cddcf6f8-1793-452b-9cc9-6d206a21333e" xlink:to="loc_us-gaap_SegmentDomain_7bca06c7-020c-4e56-8a95-90e1fc6a7931" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DiscoveryAndSafetyAssessmentSegmentMember_468f83f1-e59c-49ee-addb-56a38067e8b0" xlink:href="notv-20240930.xsd#notv_DiscoveryAndSafetyAssessmentSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_7bca06c7-020c-4e56-8a95-90e1fc6a7931" xlink:to="loc_notv_DiscoveryAndSafetyAssessmentSegmentMember_468f83f1-e59c-49ee-addb-56a38067e8b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesReportingUnitMember_48c49963-6e9e-416b-9a78-e3ab3ea3021d" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesReportingUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_7bca06c7-020c-4e56-8a95-90e1fc6a7931" xlink:to="loc_notv_ResearchModelsAndServicesReportingUnitMember_48c49963-6e9e-416b-9a78-e3ab3ea3021d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_c4450974-bd74-4f5b-beeb-576cb760ad4d" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_7bca06c7-020c-4e56-8a95-90e1fc6a7931" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_c4450974-bd74-4f5b-beeb-576cb760ad4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_14a839cc-8ca2-4d0c-8b6a-2a671bb33f05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_NumberOfReportableSegments_14a839cc-8ca2-4d0c-8b6a-2a671bb33f05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_363ffe40-5eb5-4ca2-862b-ddfcd1082561" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_363ffe40-5eb5-4ca2-862b-ddfcd1082561" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NoncashAmortizationOfInventoryFairValueStepUp_1ab95678-50cb-4962-a166-d80efaf0eb0c" xlink:href="notv-20240930.xsd#notv_NoncashAmortizationOfInventoryFairValueStepUp"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_notv_NoncashAmortizationOfInventoryFairValueStepUp_1ab95678-50cb-4962-a166-d80efaf0eb0c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_af84e692-0afd-4c4d-81fe-3d88be2892e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_af84e692-0afd-4c4d-81fe-3d88be2892e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_3f899c59-acd1-45ae-9868-85efce61f3a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_ShareBasedCompensation_3f899c59-acd1-45ae-9868-85efce61f3a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_GainLossOnFairValueRemeasurementOfConvertibleSeniorNotes_f799f635-1d9a-40e3-8b58-2046ac8c980f" xlink:href="notv-20240930.xsd#notv_GainLossOnFairValueRemeasurementOfConvertibleSeniorNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_notv_GainLossOnFairValueRemeasurementOfConvertibleSeniorNotes_f799f635-1d9a-40e3-8b58-2046ac8c980f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_f0d0c123-a5a2-45ea-840b-be78bc3d5b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_OperatingIncomeLoss_f0d0c123-a5a2-45ea-840b-be78bc3d5b1f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_e9f11b54-babd-4654-b661-5b675029f6b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_4b105346-18bd-4c59-a27c-83795f1f4971" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_e9f11b54-babd-4654-b661-5b675029f6b5" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONOperatingSegmentsRevenueandOperatingIncomeLossDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#SEGMENTANDGEOGRAPHICINFORMATIONOperatingSegmentsRevenueandOperatingIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONOperatingSegmentsRevenueandOperatingIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_059a2e44-6d1e-41b6-943f-51626740dfb2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_059a2e44-6d1e-41b6-943f-51626740dfb2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_059a2e44-6d1e-41b6-943f-51626740dfb2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2" xlink:to="loc_us-gaap_SegmentDomain_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_e920c391-0565-4445-946a-86dad7c06b64" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_6c260600-d7b2-41ca-b0b1-cb81faf3c2e2" xlink:to="loc_us-gaap_SegmentDomain_e920c391-0565-4445-946a-86dad7c06b64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DiscoveryAndSafetyAssessmentSegmentMember_ec99f366-17dd-416b-8c8e-165e788e0759" xlink:href="notv-20240930.xsd#notv_DiscoveryAndSafetyAssessmentSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e920c391-0565-4445-946a-86dad7c06b64" xlink:to="loc_notv_DiscoveryAndSafetyAssessmentSegmentMember_ec99f366-17dd-416b-8c8e-165e788e0759" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_5bf886d2-e793-41be-9827-d41020dd82c0" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e920c391-0565-4445-946a-86dad7c06b64" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_5bf886d2-e793-41be-9827-d41020dd82c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_dd48b0cb-cf20-4090-a12e-5000317d56f0" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_059a2e44-6d1e-41b6-943f-51626740dfb2" xlink:to="loc_srt_ProductOrServiceAxis_dd48b0cb-cf20-4090-a12e-5000317d56f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_dd48b0cb-cf20-4090-a12e-5000317d56f0_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_dd48b0cb-cf20-4090-a12e-5000317d56f0" xlink:to="loc_srt_ProductsAndServicesDomain_dd48b0cb-cf20-4090-a12e-5000317d56f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8016b73a-2d1d-47ee-a71f-7539432c6cd7" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_dd48b0cb-cf20-4090-a12e-5000317d56f0" xlink:to="loc_srt_ProductsAndServicesDomain_8016b73a-2d1d-47ee-a71f-7539432c6cd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_b9dfcd38-69b8-4777-a133-8967a925b820" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8016b73a-2d1d-47ee-a71f-7539432c6cd7" xlink:to="loc_us-gaap_ServiceMember_b9dfcd38-69b8-4777-a133-8967a925b820" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_810b9cee-9290-4b1f-8b40-4ccd5eb6b475" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8016b73a-2d1d-47ee-a71f-7539432c6cd7" xlink:to="loc_us-gaap_ProductMember_810b9cee-9290-4b1f-8b40-4ccd5eb6b475" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_059a2e44-6d1e-41b6-943f-51626740dfb2" xlink:to="loc_srt_ConsolidationItemsAxis_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68" xlink:to="loc_srt_ConsolidationItemsDomain_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_44aa350f-4679-4616-a582-946da6c00e40" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_feda411d-f42d-49c3-8d2e-d7b4dbd9cf68" xlink:to="loc_srt_ConsolidationItemsDomain_44aa350f-4679-4616-a582-946da6c00e40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_b3db2c76-0cf6-45ff-9eae-19b364972b8d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_44aa350f-4679-4616-a582-946da6c00e40" xlink:to="loc_us-gaap_OperatingSegmentsMember_b3db2c76-0cf6-45ff-9eae-19b364972b8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_8bf485fb-3579-4712-acf1-8ced545043b8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_44aa350f-4679-4616-a582-946da6c00e40" xlink:to="loc_us-gaap_CorporateNonSegmentMember_8bf485fb-3579-4712-acf1-8ced545043b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e9b63d5a-f93a-4e8f-bcf4-ffcd0cb10f6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e9b63d5a-f93a-4e8f-bcf4-ffcd0cb10f6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_c4143fc2-4de6-4864-8b21-c0a9d04080bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_OperatingIncomeLoss_c4143fc2-4de6-4864-8b21-c0a9d04080bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_33932bc7-d760-4bec-a250-c25f71f4a8ea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_InterestExpenseNonoperating_33932bc7-d760-4bec-a250-c25f71f4a8ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_4926e5bf-1e1e-4570-9c99-8d2e6af0c231" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_4926e5bf-1e1e-4570-9c99-8d2e6af0c231" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_15c9675a-4746-4e61-ae48-56fb37ad387f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_15c9675a-4746-4e61-ae48-56fb37ad387f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_5810983b-1904-4475-afa8-d721338cbf93" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_DepreciationAndAmortization_5810983b-1904-4475-afa8-d721338cbf93" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_d6d7c0e7-063b-4134-a304-f86c40fc4948" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_d6d7c0e7-063b-4134-a304-f86c40fc4948" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_90d60433-63da-4f05-818d-88e162e404d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_132b9bbb-f780-4563-8557-82b09779a1a7" xlink:to="loc_us-gaap_Assets_90d60433-63da-4f05-818d-88e162e404d5" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONGeographicInformationDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#SEGMENTANDGEOGRAPHICINFORMATIONGeographicInformationDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/SEGMENTANDGEOGRAPHICINFORMATIONGeographicInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_35a94963-d9a8-459a-a91d-6a6da2fc6b80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_58ca2ac1-9775-465b-959e-1248a2c033c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_35a94963-d9a8-459a-a91d-6a6da2fc6b80" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_58ca2ac1-9775-465b-959e-1248a2c033c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_d6d73e7e-b0ae-4794-99ac-709e76351586" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_58ca2ac1-9775-465b-959e-1248a2c033c3" xlink:to="loc_srt_StatementGeographicalAxis_d6d73e7e-b0ae-4794-99ac-709e76351586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_d6d73e7e-b0ae-4794-99ac-709e76351586_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_d6d73e7e-b0ae-4794-99ac-709e76351586" xlink:to="loc_srt_SegmentGeographicalDomain_d6d73e7e-b0ae-4794-99ac-709e76351586_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a582afb8-56e0-49be-8d93-e15b367f0840" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_d6d73e7e-b0ae-4794-99ac-709e76351586" xlink:to="loc_srt_SegmentGeographicalDomain_a582afb8-56e0-49be-8d93-e15b367f0840" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_361dfafd-c429-4727-890e-eeb081044939" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a582afb8-56e0-49be-8d93-e15b367f0840" xlink:to="loc_country_US_361dfafd-c429-4727-890e-eeb081044939" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_NL_599a2a63-59a6-4a0e-bc85-52f27b8da3aa" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_NL"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a582afb8-56e0-49be-8d93-e15b367f0840" xlink:to="loc_country_NL_599a2a63-59a6-4a0e-bc85-52f27b8da3aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_OtherThanUnitedStatesAndNetherlandsMember_9d9f7e8d-3f00-460a-956a-abb524830d51" xlink:href="notv-20240930.xsd#notv_OtherThanUnitedStatesAndNetherlandsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a582afb8-56e0-49be-8d93-e15b367f0840" xlink:to="loc_notv_OtherThanUnitedStatesAndNetherlandsMember_9d9f7e8d-3f00-460a-956a-abb524830d51" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_def248fe-0595-46d8-aa7f-a0b115911b33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_35a94963-d9a8-459a-a91d-6a6da2fc6b80" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_def248fe-0595-46d8-aa7f-a0b115911b33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_2cef2a02-d088-434b-9b89-08547d966a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_35a94963-d9a8-459a-a91d-6a6da2fc6b80" xlink:to="loc_us-gaap_NoncurrentAssets_2cef2a02-d088-434b-9b89-08547d966a9f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSGoodwillRollforwardDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#GOODWILLANDINTANGIBLEASSETSGoodwillRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSGoodwillRollforwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_70e4b602-85fb-407e-979a-c6077514cec5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_2361d858-7865-4d25-b66b-ae6639a8faf4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_70e4b602-85fb-407e-979a-c6077514cec5" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_2361d858-7865-4d25-b66b-ae6639a8faf4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReportingUnitAxis_d365a2a7-804c-479f-bc11-b2e660d66534" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReportingUnitAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_2361d858-7865-4d25-b66b-ae6639a8faf4" xlink:to="loc_us-gaap_ReportingUnitAxis_d365a2a7-804c-479f-bc11-b2e660d66534" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReportingUnitDomain_d365a2a7-804c-479f-bc11-b2e660d66534_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReportingUnitDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReportingUnitAxis_d365a2a7-804c-479f-bc11-b2e660d66534" xlink:to="loc_us-gaap_ReportingUnitDomain_d365a2a7-804c-479f-bc11-b2e660d66534_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReportingUnitDomain_0b59c038-d13e-4117-9365-4334b3b1c715" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReportingUnitDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReportingUnitAxis_d365a2a7-804c-479f-bc11-b2e660d66534" xlink:to="loc_us-gaap_ReportingUnitDomain_0b59c038-d13e-4117-9365-4334b3b1c715" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DiscoveryAndSafetyAssessmentReportingUnitMember_10be2c0a-4d0d-4477-986f-285f5eaacf7d" xlink:href="notv-20240930.xsd#notv_DiscoveryAndSafetyAssessmentReportingUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReportingUnitDomain_0b59c038-d13e-4117-9365-4334b3b1c715" xlink:to="loc_notv_DiscoveryAndSafetyAssessmentReportingUnitMember_10be2c0a-4d0d-4477-986f-285f5eaacf7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesReportingUnitMember_33789292-72bd-49f2-8c1c-ed903161ebd7" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesReportingUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReportingUnitDomain_0b59c038-d13e-4117-9365-4334b3b1c715" xlink:to="loc_notv_ResearchModelsAndServicesReportingUnitMember_33789292-72bd-49f2-8c1c-ed903161ebd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_70e4b602-85fb-407e-979a-c6077514cec5" xlink:to="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_89d32e98-8018-4a47-ae35-a5c9293c363d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:to="loc_us-gaap_Goodwill_89d32e98-8018-4a47-ae35-a5c9293c363d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_9cd78f90-d325-433d-b03d-c53c31fda42a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_9cd78f90-d325-433d-b03d-c53c31fda42a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_5ddb4a0c-d1ee-42ca-9d8b-b44cd8112aea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_5ddb4a0c-d1ee-42ca-9d8b-b44cd8112aea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_1bd7fbb2-08c4-4de2-8843-6797225d0715" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_0233e396-eda5-4e0b-b127-7618b3a3f807" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_1bd7fbb2-08c4-4de2-8843-6797225d0715" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_89268ce0-10ac-47b5-8c42-4ea24f3b008c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_GoodwillImpairedAccumulatedImpairmentLossAfterDeductingForeignExchangeGainLoss_d9639e00-48b0-4c04-82e8-137b0b187c85" xlink:href="notv-20240930.xsd#notv_GoodwillImpairedAccumulatedImpairmentLossAfterDeductingForeignExchangeGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_70e4b602-85fb-407e-979a-c6077514cec5" xlink:to="loc_notv_GoodwillImpairedAccumulatedImpairmentLossAfterDeductingForeignExchangeGainLoss_d9639e00-48b0-4c04-82e8-137b0b187c85" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#GOODWILLANDINTANGIBLEASSETSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_0a9615fe-9688-4570-999f-023fc505c1dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:to="loc_us-gaap_LossContingenciesTable_0a9615fe-9688-4570-999f-023fc505c1dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_f2e77d89-ded3-4931-8b3a-dc66407151f1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_0a9615fe-9688-4570-999f-023fc505c1dc" xlink:to="loc_srt_StatementGeographicalAxis_f2e77d89-ded3-4931-8b3a-dc66407151f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_f2e77d89-ded3-4931-8b3a-dc66407151f1_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_f2e77d89-ded3-4931-8b3a-dc66407151f1" xlink:to="loc_srt_SegmentGeographicalDomain_f2e77d89-ded3-4931-8b3a-dc66407151f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_2bb71e90-b165-4457-bfda-e254106d31bb" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_f2e77d89-ded3-4931-8b3a-dc66407151f1" xlink:to="loc_srt_SegmentGeographicalDomain_2bb71e90-b165-4457-bfda-e254106d31bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_KH_e6bb600b-3b7d-4500-93dc-1350880095e9" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_KH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_2bb71e90-b165-4457-bfda-e254106d31bb" xlink:to="loc_country_KH_e6bb600b-3b7d-4500-93dc-1350880095e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_49409d2b-53fc-47e1-be95-ca9466262772" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfGovernmentOfficialsIncluded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:to="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_49409d2b-53fc-47e1-be95-ca9466262772" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfImports_465190e6-48a7-48d5-af19-670875b8c23f" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfImports"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:to="loc_notv_LossContingencyNumberOfImports_465190e6-48a7-48d5-af19-670875b8c23f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_028a612d-07d2-4d68-906d-674888c05959" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_028a612d-07d2-4d68-906d-674888c05959" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_88cdb1c1-4b80-4c58-8422-47c037a1e37a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_ca3fe5d8-7ad7-415c-89a7-823800262e2d" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_88cdb1c1-4b80-4c58-8422-47c037a1e37a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSIntangibleAssetsnetbymajorclassDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#GOODWILLANDINTANGIBLEASSETSIntangibleAssetsnetbymajorclassDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSIntangibleAssetsnetbymajorclassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_849ca396-50e3-4343-b1dd-5fd330ac1378" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_29f07ea6-4267-4ac6-932e-e71e0c7aa6b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_849ca396-50e3-4343-b1dd-5fd330ac1378" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_29f07ea6-4267-4ac6-932e-e71e0c7aa6b2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_29f07ea6-4267-4ac6-932e-e71e0c7aa6b2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1850da46-7dde-44c5-bb09-735fc1c936e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_69283a5a-b7ad-4bdd-9316-7f9d4a06a5e7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1850da46-7dde-44c5-bb09-735fc1c936e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_6d1aad9c-f614-4d35-8fb7-a215f64a14f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1850da46-7dde-44c5-bb09-735fc1c936e5" xlink:to="loc_us-gaap_CustomerRelationshipsMember_6d1aad9c-f614-4d35-8fb7-a215f64a14f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_0afb6134-cd1a-4d29-9e0f-9c179ce025b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1850da46-7dde-44c5-bb09-735fc1c936e5" xlink:to="loc_us-gaap_IntellectualPropertyMember_0afb6134-cd1a-4d29-9e0f-9c179ce025b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_5f6dcd1c-8e93-41ea-a962-ff139741d445" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1850da46-7dde-44c5-bb09-735fc1c936e5" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_5f6dcd1c-8e93-41ea-a962-ff139741d445" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_16a9ef47-730e-4594-b1a1-75ce5de5cd23" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_849ca396-50e3-4343-b1dd-5fd330ac1378" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_16a9ef47-730e-4594-b1a1-75ce5de5cd23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_9e39cf52-33be-4827-a0ae-f14582efeec5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_849ca396-50e3-4343-b1dd-5fd330ac1378" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_9e39cf52-33be-4827-a0ae-f14582efeec5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_740ce972-398e-4432-a9cc-dbabbdbe50ab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_849ca396-50e3-4343-b1dd-5fd330ac1378" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_740ce972-398e-4432-a9cc-dbabbdbe50ab" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSAmortizationofintangibleassetsDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#GOODWILLANDINTANGIBLEASSETSAmortizationofintangibleassetsDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/GOODWILLANDINTANGIBLEASSETSAmortizationofintangibleassetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_b22b8b84-cbf0-44ee-b47d-4eb92e61296f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9f13458b-c1bb-4f7d-b391-c1157e5d2370" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_b22b8b84-cbf0-44ee-b47d-4eb92e61296f" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9f13458b-c1bb-4f7d-b391-c1157e5d2370" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee907aa0-41bb-4463-b552-8fc812fcd44f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9f13458b-c1bb-4f7d-b391-c1157e5d2370" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee907aa0-41bb-4463-b552-8fc812fcd44f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ee907aa0-41bb-4463-b552-8fc812fcd44f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee907aa0-41bb-4463-b552-8fc812fcd44f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ee907aa0-41bb-4463-b552-8fc812fcd44f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bdcd4369-b1b8-46c3-b034-47ea76568aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee907aa0-41bb-4463-b552-8fc812fcd44f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bdcd4369-b1b8-46c3-b034-47ea76568aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_e26791b0-c708-40b4-bc2d-d118ad9be216" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bdcd4369-b1b8-46c3-b034-47ea76568aa8" xlink:to="loc_us-gaap_CustomerRelationshipsMember_e26791b0-c708-40b4-bc2d-d118ad9be216" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_50a86ec7-b916-4b68-a7bc-42fd0a94aa83" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bdcd4369-b1b8-46c3-b034-47ea76568aa8" xlink:to="loc_us-gaap_IntellectualPropertyMember_50a86ec7-b916-4b68-a7bc-42fd0a94aa83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_a9e7dbf8-59b7-49ab-9efd-733e4953b5f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bdcd4369-b1b8-46c3-b034-47ea76568aa8" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_a9e7dbf8-59b7-49ab-9efd-733e4953b5f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_9f13458b-c1bb-4f7d-b391-c1157e5d2370" xlink:to="loc_srt_RangeAxis_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6" xlink:to="loc_srt_RangeMember_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_85e6f788-f857-4e2b-bac7-ea647e08d416" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_8eb45a6d-86ea-4eeb-b802-bf88fb4291b6" xlink:to="loc_srt_RangeMember_85e6f788-f857-4e2b-bac7-ea647e08d416" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_2da74814-fbef-46a5-b8bd-f36d7cc8948e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_85e6f788-f857-4e2b-bac7-ea647e08d416" xlink:to="loc_srt_WeightedAverageMember_2da74814-fbef-46a5-b8bd-f36d7cc8948e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_b22b8b84-cbf0-44ee-b47d-4eb92e61296f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2e4186fd-1849-4553-85c4-9d1801d23f33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2e4186fd-1849-4553-85c4-9d1801d23f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_9c680517-173b-4a05-8d68-acd383e7aef3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_9c680517-173b-4a05-8d68-acd383e7aef3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_a34c832a-ef65-4696-ae8c-0298984619ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_a34c832a-ef65-4696-ae8c-0298984619ed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_0a8b2e79-459c-47b9-9da4-b28488439cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_0a8b2e79-459c-47b9-9da4-b28488439cd8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_7024e792-be87-459e-baf2-382cb5356cc8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_7024e792-be87-459e-baf2-382cb5356cc8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_47338de6-5583-46b3-91dd-ce05c1e251c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_47338de6-5583-46b3-91dd-ce05c1e251c3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_488b49d2-09d2-4005-9d66-902b510b49e8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_488b49d2-09d2-4005-9d66-902b510b49e8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d05239f1-ccb1-4f1a-ba67-80c2b9db86cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_13b69d70-2684-4f33-ada9-e391018e6f8d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d05239f1-ccb1-4f1a-ba67-80c2b9db86cd" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTScheduleoflongtermdebtDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTScheduleoflongtermdebtDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTScheduleoflongtermdebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_394e3abc-e44e-4be2-9b0d-943154043227" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_DebtInstrumentTable_394e3abc-e44e-4be2-9b0d-943154043227" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_936ced13-ad49-496c-bf4e-04e66af82fc5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_394e3abc-e44e-4be2-9b0d-943154043227" xlink:to="loc_us-gaap_DebtInstrumentAxis_936ced13-ad49-496c-bf4e-04e66af82fc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_936ced13-ad49-496c-bf4e-04e66af82fc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_936ced13-ad49-496c-bf4e-04e66af82fc5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_936ced13-ad49-496c-bf4e-04e66af82fc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_936ced13-ad49-496c-bf4e-04e66af82fc5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteBolderBiopathMember_6ba2de52-27be-462f-8647-65e6f4863fdb" xlink:href="notv-20240930.xsd#notv_SellerNoteBolderBiopathMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerNoteBolderBiopathMember_6ba2de52-27be-462f-8647-65e6f4863fdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNotePreClinicalResearchServicesMember_84b34a12-4061-4d7a-9f6e-36bd55c240d1" xlink:href="notv-20240930.xsd#notv_SellerNotePreClinicalResearchServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerNotePreClinicalResearchServicesMember_84b34a12-4061-4d7a-9f6e-36bd55c240d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNotePlatoBiopharmaMember_ad00fc0d-a245-4182-a362-150edd975ff4" xlink:href="notv-20240930.xsd#notv_SellerNotePlatoBiopharmaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerNotePlatoBiopharmaMember_ad00fc0d-a245-4182-a362-150edd975ff4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerPayableOrientBioResourceCenterMember_ab693154-1db7-4e47-b97a-b9879e9714f7" xlink:href="notv-20240930.xsd#notv_SellerPayableOrientBioResourceCenterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerPayableOrientBioResourceCenterMember_ab693154-1db7-4e47-b97a-b9879e9714f7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteHistionMember_ddfe4fc5-eed4-4db1-aac1-b1e7bc4df686" xlink:href="notv-20240930.xsd#notv_SellerNoteHistionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerNoteHistionMember_ddfe4fc5-eed4-4db1-aac1-b1e7bc4df686" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteProtypiaMember_bdcffc70-63b4-4977-a9a3-25df483b3490" xlink:href="notv-20240930.xsd#notv_SellerNoteProtypiaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SellerNoteProtypiaMember_bdcffc70-63b4-4977-a9a3-25df483b3490" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_EconomicInjuryDisasterLoanSmallBusinessAdministrationMember_c23fea38-bdd5-44d3-85cd-c0758667e22e" xlink:href="notv-20240930.xsd#notv_EconomicInjuryDisasterLoanSmallBusinessAdministrationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_EconomicInjuryDisasterLoanSmallBusinessAdministrationMember_c23fea38-bdd5-44d3-85cd-c0758667e22e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_e20928f3-5dbf-48f4-b771-834f7d6bd51d" xlink:href="notv-20240930.xsd#notv_SeniorSecuredSecondLienPIKNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_e20928f3-5dbf-48f4-b771-834f7d6bd51d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleSeniorNotesMember_818484b1-dac4-4a9a-adbe-16d509d8b111" xlink:href="notv-20240930.xsd#notv_ConvertibleSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_ConvertibleSeniorNotesMember_818484b1-dac4-4a9a-adbe-16d509d8b111" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_f16610d1-3a7f-4316-8fc0-c14bccbdc2c8" xlink:href="notv-20240930.xsd#notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c8c3e8ea-b8f4-4574-8d38-a8ed235fec23" xlink:to="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_f16610d1-3a7f-4316-8fc0-c14bccbdc2c8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_df8a32e7-0dc1-4125-8ea3-82817a3318f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_394e3abc-e44e-4be2-9b0d-943154043227" xlink:to="loc_us-gaap_CreditFacilityAxis_df8a32e7-0dc1-4125-8ea3-82817a3318f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_df8a32e7-0dc1-4125-8ea3-82817a3318f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_df8a32e7-0dc1-4125-8ea3-82817a3318f1" xlink:to="loc_us-gaap_CreditFacilityDomain_df8a32e7-0dc1-4125-8ea3-82817a3318f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_df7cc174-597a-493d-b3eb-f7f7ce1ef2f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_df8a32e7-0dc1-4125-8ea3-82817a3318f1" xlink:to="loc_us-gaap_CreditFacilityDomain_df7cc174-597a-493d-b3eb-f7f7ce1ef2f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TermLoanMember_1f61be8c-b07a-464f-8a5e-6035ab9b6750" xlink:href="notv-20240930.xsd#notv_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_df7cc174-597a-493d-b3eb-f7f7ce1ef2f3" xlink:to="loc_notv_TermLoanMember_1f61be8c-b07a-464f-8a5e-6035ab9b6750" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NewDelayedDrawTermLoanMember_260a8570-8c1f-4bde-86a1-ebb5b3f8360f" xlink:href="notv-20240930.xsd#notv_NewDelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_df7cc174-597a-493d-b3eb-f7f7ce1ef2f3" xlink:to="loc_notv_NewDelayedDrawTermLoanMember_260a8570-8c1f-4bde-86a1-ebb5b3f8360f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_3531ad17-7e00-46a9-838a-8caf282e49c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_df7cc174-597a-493d-b3eb-f7f7ce1ef2f3" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_3531ad17-7e00-46a9-838a-8caf282e49c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_290f54d8-01aa-4e9e-a913-449492bc4a9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_290f54d8-01aa-4e9e-a913-449492bc4a9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_5a13ed8f-13a2-4c8c-80a0-28ddd6b1115b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_5a13ed8f-13a2-4c8c-80a0-28ddd6b1115b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_dd79a906-7448-47b4-9af9-8d37cbd64f4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_LongTermDebt_dd79a906-7448-47b4-9af9-8d37cbd64f4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_c4aa2d5f-df7d-41ff-a14e-676484b887e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_LongTermDebtCurrent_c4aa2d5f-df7d-41ff-a14e-676484b887e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_04621ef6-3c78-4a8d-8f03-61d33331ecdb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_04621ef6-3c78-4a8d-8f03-61d33331ecdb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_16adc102-785d-479f-93fc-930f3213bf8f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c0f096d5-e1c0-42b0-a27d-70abef5f14fd" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_16adc102-785d-479f-93fc-930f3213bf8f" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTSignificantTransactionsNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTSignificantTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTSignificantTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_7a31717a-fa7c-49bf-a3ce-07e117c502a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:to="loc_us-gaap_CreditFacilityAxis_7a31717a-fa7c-49bf-a3ce-07e117c502a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_7a31717a-fa7c-49bf-a3ce-07e117c502a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_7a31717a-fa7c-49bf-a3ce-07e117c502a2" xlink:to="loc_us-gaap_CreditFacilityDomain_7a31717a-fa7c-49bf-a3ce-07e117c502a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_fed1ed58-ca45-42b6-9a3f-c46143031fad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_7a31717a-fa7c-49bf-a3ce-07e117c502a2" xlink:to="loc_us-gaap_CreditFacilityDomain_fed1ed58-ca45-42b6-9a3f-c46143031fad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NewDelayedDrawTermLoanMember_852b5aa0-8d5b-48fb-a595-42853896517a" xlink:href="notv-20240930.xsd#notv_NewDelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_fed1ed58-ca45-42b6-9a3f-c46143031fad" xlink:to="loc_notv_NewDelayedDrawTermLoanMember_852b5aa0-8d5b-48fb-a595-42853896517a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_57f0d2f5-1f02-433c-a4c3-1351b3870cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_fed1ed58-ca45-42b6-9a3f-c46143031fad" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_57f0d2f5-1f02-433c-a4c3-1351b3870cd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_c6c6eab1-f3e2-4308-8725-d06695fa3e6d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:to="loc_srt_CounterpartyNameAxis_c6c6eab1-f3e2-4308-8725-d06695fa3e6d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_c6c6eab1-f3e2-4308-8725-d06695fa3e6d_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_c6c6eab1-f3e2-4308-8725-d06695fa3e6d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_c6c6eab1-f3e2-4308-8725-d06695fa3e6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9d86620f-e708-4be9-8382-c7381076e458" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_c6c6eab1-f3e2-4308-8725-d06695fa3e6d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9d86620f-e708-4be9-8382-c7381076e458" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeventhAmendmentPurchasersMember_e51d97c6-fd8e-4580-9252-6614a6b1a9fb" xlink:href="notv-20240930.xsd#notv_SeventhAmendmentPurchasersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9d86620f-e708-4be9-8382-c7381076e458" xlink:to="loc_notv_SeventhAmendmentPurchasersMember_e51d97c6-fd8e-4580-9252-6614a6b1a9fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeventhAmendmentStructuringAgentMember_b5e98171-f4ce-4b25-8866-99362514d1df" xlink:href="notv-20240930.xsd#notv_SeventhAmendmentStructuringAgentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_9d86620f-e708-4be9-8382-c7381076e458" xlink:to="loc_notv_SeventhAmendmentStructuringAgentMember_b5e98171-f4ce-4b25-8866-99362514d1df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1866251e-3851-4eaf-b827-e185d5beabac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:to="loc_us-gaap_DebtInstrumentAxis_1866251e-3851-4eaf-b827-e185d5beabac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1866251e-3851-4eaf-b827-e185d5beabac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1866251e-3851-4eaf-b827-e185d5beabac" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1866251e-3851-4eaf-b827-e185d5beabac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_83b5ea91-9d7f-4766-8007-4301214cc98e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1866251e-3851-4eaf-b827-e185d5beabac" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_83b5ea91-9d7f-4766-8007-4301214cc98e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_c7816849-67c0-4cda-bc9c-3f3522b43c03" xlink:href="notv-20240930.xsd#notv_SeniorSecuredSecondLienPIKNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_83b5ea91-9d7f-4766-8007-4301214cc98e" xlink:to="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_c7816849-67c0-4cda-bc9c-3f3522b43c03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleSeniorNotesMember_2ebded44-79eb-4ed4-a088-94351be4bc40" xlink:href="notv-20240930.xsd#notv_ConvertibleSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_83b5ea91-9d7f-4766-8007-4301214cc98e" xlink:to="loc_notv_ConvertibleSeniorNotesMember_2ebded44-79eb-4ed4-a088-94351be4bc40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_0e4bb579-d61f-4048-9f7d-61681a2235c2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6b34ef14-6c8e-4e3c-9137-2d853a6853dd" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_0e4bb579-d61f-4048-9f7d-61681a2235c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0e4bb579-d61f-4048-9f7d-61681a2235c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0e4bb579-d61f-4048-9f7d-61681a2235c2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0e4bb579-d61f-4048-9f7d-61681a2235c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_98749756-9ccf-4a6b-88c6-356526ef1894" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0e4bb579-d61f-4048-9f7d-61681a2235c2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_98749756-9ccf-4a6b-88c6-356526ef1894" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_86e7c2e0-ccfe-43bb-85da-58a934a8657b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_98749756-9ccf-4a6b-88c6-356526ef1894" xlink:to="loc_us-gaap_SecuredDebtMember_86e7c2e0-ccfe-43bb-85da-58a934a8657b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_b83d55df-9346-46c9-9ba9-1c2f94652a81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_98749756-9ccf-4a6b-88c6-356526ef1894" xlink:to="loc_us-gaap_ConvertibleDebtMember_b83d55df-9346-46c9-9ba9-1c2f94652a81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_09eb71da-318c-4fc4-93ff-dcc66e1dd7ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_09eb71da-318c-4fc4-93ff-dcc66e1dd7ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_0585bcf1-07b2-4d6f-ad5d-a6e3ceb347ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_0585bcf1-07b2-4d6f-ad5d-a6e3ceb347ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_5191fb91-3564-48e5-a0ff-38a72a63bcde" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_5191fb91-3564-48e5-a0ff-38a72a63bcde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_24fe3c4b-b819-4bf2-8dbe-536a4f44825a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_24fe3c4b-b819-4bf2-8dbe-536a4f44825a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_227d7d1e-f209-4c5f-b530-849c55ce0ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_227d7d1e-f209-4c5f-b530-849c55ce0ce4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_c513de73-2c7d-4382-a9c5-bbb39dcbb0ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_c513de73-2c7d-4382-a9c5-bbb39dcbb0ba" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_4ed63bc4-cf34-4a2c-be85-c521fe72f08c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_4ed63bc4-cf34-4a2c-be85-c521fe72f08c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_e8cbb43e-3734-4168-8c1d-211e9f80af93" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_LongTermDebt_e8cbb43e-3734-4168-8c1d-211e9f80af93" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_730aeb95-34f2-4644-a000-cc788ef1051b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_287ce3ec-8877-499a-b035-cd31c64aad26" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_730aeb95-34f2-4644-a000-cc788ef1051b" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTFairValueNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTFairValueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTFairValueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_DebtInstrumentAxis_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c35ddf5f-7e28-4e96-928b-d06b1b747653" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_c5a7f9fd-5dba-4f01-90dd-2172d67cd2bd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c35ddf5f-7e28-4e96-928b-d06b1b747653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_52ea4523-f17b-460c-9654-5f7c760d77c5" xlink:href="notv-20240930.xsd#notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c35ddf5f-7e28-4e96-928b-d06b1b747653" xlink:to="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_52ea4523-f17b-460c-9654-5f7c760d77c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleSeniorNotesMember_267e0dcc-33cd-47c5-ae00-98dbf914e375" xlink:href="notv-20240930.xsd#notv_ConvertibleSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c35ddf5f-7e28-4e96-928b-d06b1b747653" xlink:to="loc_notv_ConvertibleSeniorNotesMember_267e0dcc-33cd-47c5-ae00-98dbf914e375" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_214211e6-8b9e-45f9-98bd-4950b790c491" xlink:href="notv-20240930.xsd#notv_SeniorSecuredSecondLienPIKNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c35ddf5f-7e28-4e96-928b-d06b1b747653" xlink:to="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_214211e6-8b9e-45f9-98bd-4950b790c491" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_10db0e1c-7d95-4031-9bb1-960c2d7aac5a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_10db0e1c-7d95-4031-9bb1-960c2d7aac5a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_10db0e1c-7d95-4031-9bb1-960c2d7aac5a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_10db0e1c-7d95-4031-9bb1-960c2d7aac5a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_10db0e1c-7d95-4031-9bb1-960c2d7aac5a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0ff49784-1bf5-4255-aa58-f460cf627d82" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_10db0e1c-7d95-4031-9bb1-960c2d7aac5a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0ff49784-1bf5-4255-aa58-f460cf627d82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_76c64338-e8a2-4b85-928f-a51958e35c76" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0ff49784-1bf5-4255-aa58-f460cf627d82" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_76c64338-e8a2-4b85-928f-a51958e35c76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d74b6099-8a12-4f63-996d-acc7c7c4da38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_CreditFacilityAxis_d74b6099-8a12-4f63-996d-acc7c7c4da38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d74b6099-8a12-4f63-996d-acc7c7c4da38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d74b6099-8a12-4f63-996d-acc7c7c4da38" xlink:to="loc_us-gaap_CreditFacilityDomain_d74b6099-8a12-4f63-996d-acc7c7c4da38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_4988c3b9-9729-4d39-97d9-6415c7e6f9dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d74b6099-8a12-4f63-996d-acc7c7c4da38" xlink:to="loc_us-gaap_CreditFacilityDomain_4988c3b9-9729-4d39-97d9-6415c7e6f9dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_8a3910b0-15f1-429a-b02b-46f81fd54a15" xlink:href="notv-20240930.xsd#notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_4988c3b9-9729-4d39-97d9-6415c7e6f9dd" xlink:to="loc_notv_TermLoanFacilityInitialDDTLAndIncrementalTermLoansMember_8a3910b0-15f1-429a-b02b-46f81fd54a15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_37bcd38f-271c-41f0-914a-4f24a30839a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_37bcd38f-271c-41f0-914a-4f24a30839a8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_37bcd38f-271c-41f0-914a-4f24a30839a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_37bcd38f-271c-41f0-914a-4f24a30839a8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_37bcd38f-271c-41f0-914a-4f24a30839a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_17dd6ab2-712d-41a4-8e4a-e7414cf032b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_37bcd38f-271c-41f0-914a-4f24a30839a8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_17dd6ab2-712d-41a4-8e4a-e7414cf032b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_a739fee2-8de2-415b-8cef-308951059797" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_17dd6ab2-712d-41a4-8e4a-e7414cf032b1" xlink:to="loc_us-gaap_SecuredDebtMember_a739fee2-8de2-415b-8cef-308951059797" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_a28af068-2729-4ad0-95b1-9217c1479edb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_a28af068-2729-4ad0-95b1-9217c1479edb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_a28af068-2729-4ad0-95b1-9217c1479edb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_a28af068-2729-4ad0-95b1-9217c1479edb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_a28af068-2729-4ad0-95b1-9217c1479edb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_43632105-2f19-4e54-9eb3-d230426667a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_a28af068-2729-4ad0-95b1-9217c1479edb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_43632105-2f19-4e54-9eb3-d230426667a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_4ac3fac5-5237-4482-af72-d0a03c80b23f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_43632105-2f19-4e54-9eb3-d230426667a2" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_4ac3fac5-5237-4482-af72-d0a03c80b23f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_8b522755-5ae1-4b6f-996c-cb843564daa5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_43632105-2f19-4e54-9eb3-d230426667a2" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_8b522755-5ae1-4b6f-996c-cb843564daa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_7fb422dc-7c92-457f-8071-076f5641fd2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_7fb422dc-7c92-457f-8071-076f5641fd2d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_7fb422dc-7c92-457f-8071-076f5641fd2d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_7fb422dc-7c92-457f-8071-076f5641fd2d" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_7fb422dc-7c92-457f-8071-076f5641fd2d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_cec22c47-b221-4d25-8b33-cf644598cbd5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_7fb422dc-7c92-457f-8071-076f5641fd2d" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_cec22c47-b221-4d25-8b33-cf644598cbd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_3c8a38a2-accb-45d7-8b1c-a6bbeeebefd1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_cec22c47-b221-4d25-8b33-cf644598cbd5" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_3c8a38a2-accb-45d7-8b1c-a6bbeeebefd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_534d8688-9dc8-44f5-a5c0-143105ffc258" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_cec22c47-b221-4d25-8b33-cf644598cbd5" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_534d8688-9dc8-44f5-a5c0-143105ffc258" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputCreditSpreadMember_48b183c6-c179-4849-b671-e7ed4bde1da0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputCreditSpreadMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_cec22c47-b221-4d25-8b33-cf644598cbd5" xlink:to="loc_us-gaap_MeasurementInputCreditSpreadMember_48b183c6-c179-4849-b671-e7ed4bde1da0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_64a44a70-e53e-4c07-8ece-ffcfbcae41ac" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f6159e1b-e5d5-4553-a28e-88e16b8996ac" xlink:to="loc_srt_CounterpartyNameAxis_64a44a70-e53e-4c07-8ece-ffcfbcae41ac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_64a44a70-e53e-4c07-8ece-ffcfbcae41ac_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_64a44a70-e53e-4c07-8ece-ffcfbcae41ac" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_64a44a70-e53e-4c07-8ece-ffcfbcae41ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_56520d05-7cec-4b8b-9b7f-a1f6654ee17a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_64a44a70-e53e-4c07-8ece-ffcfbcae41ac" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_56520d05-7cec-4b8b-9b7f-a1f6654ee17a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeventhAmendmentPurchasersMember_f19aa2e3-4313-4e31-9e87-7f604672052d" xlink:href="notv-20240930.xsd#notv_SeventhAmendmentPurchasersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_56520d05-7cec-4b8b-9b7f-a1f6654ee17a" xlink:to="loc_notv_SeventhAmendmentPurchasersMember_f19aa2e3-4313-4e31-9e87-7f604672052d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_e715d93a-e54e-4343-aba8-311e6a72a149" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_LongTermDebtFairValue_e715d93a-e54e-4343-aba8-311e6a72a149" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentMeasurementInput_1d7136ab-c22b-47b9-9030-c1ee9d4d7948" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_DebtInstrumentMeasurementInput_1d7136ab-c22b-47b9-9030-c1ee9d4d7948" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aa61be00-7079-40c2-9093-00cfab4a3b78" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aa61be00-7079-40c2-9093-00cfab4a3b78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_edb7e82e-11db-497f-be33-ae5a5c0a6ec1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_edb7e82e-11db-497f-be33-ae5a5c0a6ec1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_d19db741-20a5-40a2-b266-3137f124bc81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5308faf4-baef-4329-bef0-28d1d7032f69" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_d19db741-20a5-40a2-b266-3137f124bc81" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTRevolvingCreditFacilityandAmendmentsNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTRevolvingCreditFacilityandAmendmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTRevolvingCreditFacilityandAmendmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_25aa89fc-3749-4aef-acf9-f62647412cb2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_us-gaap_CreditFacilityAxis_25aa89fc-3749-4aef-acf9-f62647412cb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_25aa89fc-3749-4aef-acf9-f62647412cb2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_25aa89fc-3749-4aef-acf9-f62647412cb2" xlink:to="loc_us-gaap_CreditFacilityDomain_25aa89fc-3749-4aef-acf9-f62647412cb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_25aa89fc-3749-4aef-acf9-f62647412cb2" xlink:to="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_56ee26ba-d60c-40f2-925c-2b33f6c02f42" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_56ee26ba-d60c-40f2-925c-2b33f6c02f42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AmendedAndRestatedCreditAgreementMember_47a519b1-1174-46a0-bbdf-50719af58197" xlink:href="notv-20240930.xsd#notv_AmendedAndRestatedCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:to="loc_notv_AmendedAndRestatedCreditAgreementMember_47a519b1-1174-46a0-bbdf-50719af58197" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_b62efb9c-1910-40a3-b405-73c847f4dbe4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_b62efb9c-1910-40a3-b405-73c847f4dbe4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TermLoanMember_4d171e76-982b-48a7-ac6c-0fb2312d54a0" xlink:href="notv-20240930.xsd#notv_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:to="loc_notv_TermLoanMember_4d171e76-982b-48a7-ac6c-0fb2312d54a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NewDelayedDrawTermLoanMember_9be3338d-4f27-4157-8250-68517318ce94" xlink:href="notv-20240930.xsd#notv_NewDelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_c008b365-f552-4776-96e8-a36e7277539a" xlink:to="loc_notv_NewDelayedDrawTermLoanMember_9be3338d-4f27-4157-8250-68517318ce94" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b1d41876-a8d8-4588-8d95-78c74235323e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_srt_RangeAxis_b1d41876-a8d8-4588-8d95-78c74235323e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b1d41876-a8d8-4588-8d95-78c74235323e_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b1d41876-a8d8-4588-8d95-78c74235323e" xlink:to="loc_srt_RangeMember_b1d41876-a8d8-4588-8d95-78c74235323e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_329ac812-6c44-4370-b833-7599e6020200" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b1d41876-a8d8-4588-8d95-78c74235323e" xlink:to="loc_srt_RangeMember_329ac812-6c44-4370-b833-7599e6020200" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_7a72a05f-493e-4129-893c-2ac4c0583e6a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_329ac812-6c44-4370-b833-7599e6020200" xlink:to="loc_srt_MinimumMember_7a72a05f-493e-4129-893c-2ac4c0583e6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_75079a61-6307-4b70-9c13-2d85898c76ac" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_329ac812-6c44-4370-b833-7599e6020200" xlink:to="loc_srt_MaximumMember_75079a61-6307-4b70-9c13-2d85898c76ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_09df0cc0-032e-4c3b-96f4-407f97d82d05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_us-gaap_VariableRateAxis_09df0cc0-032e-4c3b-96f4-407f97d82d05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_09df0cc0-032e-4c3b-96f4-407f97d82d05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_09df0cc0-032e-4c3b-96f4-407f97d82d05" xlink:to="loc_us-gaap_VariableRateDomain_09df0cc0-032e-4c3b-96f4-407f97d82d05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_09df0cc0-032e-4c3b-96f4-407f97d82d05" xlink:to="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrimeRateMember_aa671df6-6768-4651-86ab-fe523f5aa424" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrimeRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:to="loc_us-gaap_PrimeRateMember_aa671df6-6768-4651-86ab-fe523f5aa424" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LondonInterbankOfferedRateMember_9954f8ec-6f9f-4f4b-a39c-6d011bf9d464" xlink:href="notv-20240930.xsd#notv_LondonInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:to="loc_notv_LondonInterbankOfferedRateMember_9954f8ec-6f9f-4f4b-a39c-6d011bf9d464" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_7dbe9c45-aef8-450c-abc5-376d4b07438e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_7dbe9c45-aef8-450c-abc5-376d4b07438e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_4fe7685d-39d8-4de4-9c1d-dbcf5b93d033" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_8d6175ad-0355-4d9c-9910-102e4eed6b45" xlink:to="loc_us-gaap_BaseRateMember_4fe7685d-39d8-4de4-9c1d-dbcf5b93d033" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantAxis_990a636e-d9e4-4aaf-910f-f87be245c772" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_notv_DebtInstrumentCovenantAxis_990a636e-d9e4-4aaf-910f-f87be245c772" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantDomain_990a636e-d9e4-4aaf-910f-f87be245c772_default" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_notv_DebtInstrumentCovenantAxis_990a636e-d9e4-4aaf-910f-f87be245c772" xlink:to="loc_notv_DebtInstrumentCovenantDomain_990a636e-d9e4-4aaf-910f-f87be245c772_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_notv_DebtInstrumentCovenantAxis_990a636e-d9e4-4aaf-910f-f87be245c772" xlink:to="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingSeptember302023Member_3e92be09-587e-4e27-bd7f-46cf9c9ebf21" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingSeptember302023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingSeptember302023Member_3e92be09-587e-4e27-bd7f-46cf9c9ebf21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingMarch312025Member_73495e57-6411-4b7f-b76c-9d47ab5f1bf0" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingMarch312025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_LineOfCreditFacilityLeverageRatioToBeMaintainedBeginningQuarterEndingMarch312025Member_73495e57-6411-4b7f-b76c-9d47ab5f1bf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedDuringFirstAnniversaryMember_80b04d7e-b09c-40ec-af52-554b74811aae" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedDuringFirstAnniversaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedDuringFirstAnniversaryMember_80b04d7e-b09c-40ec-af52-554b74811aae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedFromAndAfterFirstAnniversaryMember_1527ee03-2c6e-4a6a-8f57-07ec4ab933b5" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedFromAndAfterFirstAnniversaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_LineOfCreditFacilityMinimumFixedChargeCoverageRatioToBeMaintainedFromAndAfterFirstAnniversaryMember_1527ee03-2c6e-4a6a-8f57-07ec4ab933b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodOneMember_a2530b39-2a81-4137-9355-5863dad0512b" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantWeeklyLiquidityPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodOneMember_a2530b39-2a81-4137-9355-5863dad0512b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodTwoMember_ec549546-72a3-4c3c-90cf-7406656a821b" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantWeeklyLiquidityPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodTwoMember_ec549546-72a3-4c3c-90cf-7406656a821b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodThreeMember_a4cdf98c-994b-4bc5-8570-74100fcebddf" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantWeeklyLiquidityPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenantWeeklyLiquidityPeriodThreeMember_a4cdf98c-994b-4bc5-8570-74100fcebddf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantPeriodAmendmentReliefPeriodMember_b597c2db-17f3-4b7d-82d7-16c03690ff65" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantPeriodAmendmentReliefPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenantPeriodAmendmentReliefPeriodMember_b597c2db-17f3-4b7d-82d7-16c03690ff65" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantPeriodAfterAmendmentReliefPeriodMember_bb626eac-87e1-496e-b111-433c8568515c" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantPeriodAfterAmendmentReliefPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenantPeriodAfterAmendmentReliefPeriodMember_bb626eac-87e1-496e-b111-433c8568515c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenant2024SettlementMember_0a58ccda-ed8c-46f2-8469-ee24c15826b6" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenant2024SettlementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_DebtInstrumentCovenantDomain_ec61a389-0f8b-49fd-8643-9347eb19deda" xlink:to="loc_notv_DebtInstrumentCovenant2024SettlementMember_0a58ccda-ed8c-46f2-8469-ee24c15826b6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_7a233857-297b-4816-b02b-4ec5e3a5088a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_us-gaap_DebtInstrumentAxis_7a233857-297b-4816-b02b-4ec5e3a5088a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7a233857-297b-4816-b02b-4ec5e3a5088a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_7a233857-297b-4816-b02b-4ec5e3a5088a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7a233857-297b-4816-b02b-4ec5e3a5088a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6febbc20-89af-48c2-9eee-5e01b170f1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_7a233857-297b-4816-b02b-4ec5e3a5088a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6febbc20-89af-48c2-9eee-5e01b170f1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_dbb07bdb-91c3-4d4a-b098-1b9559b64e20" xlink:href="notv-20240930.xsd#notv_SeniorSecuredSecondLienPIKNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6febbc20-89af-48c2-9eee-5e01b170f1cb" xlink:to="loc_notv_SeniorSecuredSecondLienPIKNotesDue2027Member_dbb07bdb-91c3-4d4a-b098-1b9559b64e20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_db7ee8b0-6f7d-441c-bf1a-76ab97a4a82e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_ed9a1745-a3a1-47da-a5c1-430f7f4a04cc" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_db7ee8b0-6f7d-441c-bf1a-76ab97a4a82e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_4d0fc7e1-ab4e-47cf-b259-70c7d8e13abc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_db7ee8b0-6f7d-441c-bf1a-76ab97a4a82e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_4d0fc7e1-ab4e-47cf-b259-70c7d8e13abc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_4a0e1839-e4c6-4149-aeaa-90b31fd0faf7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_db7ee8b0-6f7d-441c-bf1a-76ab97a4a82e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_4a0e1839-e4c6-4149-aeaa-90b31fd0faf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_49be4d36-5a4f-4167-8796-547b6f9fb421" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_db7ee8b0-6f7d-441c-bf1a-76ab97a4a82e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_49be4d36-5a4f-4167-8796-547b6f9fb421" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_ee4ec39c-d282-41e7-820b-850ac4b0e476" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a5cb1354-039a-49bc-9aff-1b75d35693b1" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_ee4ec39c-d282-41e7-820b-850ac4b0e476" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ee4ec39c-d282-41e7-820b-850ac4b0e476_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ee4ec39c-d282-41e7-820b-850ac4b0e476" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ee4ec39c-d282-41e7-820b-850ac4b0e476_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_1c1070d8-d2bf-407f-9647-dbbd99112c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ee4ec39c-d282-41e7-820b-850ac4b0e476" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_1c1070d8-d2bf-407f-9647-dbbd99112c1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_650dd4a0-941c-4354-b69a-2e90465af0e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_1c1070d8-d2bf-407f-9647-dbbd99112c1f" xlink:to="loc_us-gaap_SecuredDebtMember_650dd4a0-941c-4354-b69a-2e90465af0e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_c5df827d-9edf-4e63-a32f-8b4a15cea58b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCredit_c5df827d-9edf-4e63-a32f-8b4a15cea58b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_fe047ffa-1362-40ed-a009-78da6fdbc103" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_fe047ffa-1362-40ed-a009-78da6fdbc103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_3f9ea73d-db70-4d7c-b80c-a026ac267f66" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_3f9ea73d-db70-4d7c-b80c-a026ac267f66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_07e0874e-af03-49dd-be4e-eacec56e13f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_07e0874e-af03-49dd-be4e-eacec56e13f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityPrepaymentPremiumPercentage_2bc32b2a-f416-4e23-950f-eca348add2c6" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityPrepaymentPremiumPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_LineOfCreditFacilityPrepaymentPremiumPercentage_2bc32b2a-f416-4e23-950f-eca348add2c6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LineOfCreditFacilityThresholdSecuredLeverageRatio_5c6b1685-5905-458f-8d2c-13b7db273030" xlink:href="notv-20240930.xsd#notv_LineOfCreditFacilityThresholdSecuredLeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_LineOfCreditFacilityThresholdSecuredLeverageRatio_5c6b1685-5905-458f-8d2c-13b7db273030" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_7465c0bb-85ab-4593-b47b-183f7c2bf29f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_7465c0bb-85ab-4593-b47b-183f7c2bf29f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_d92561a1-d27f-4699-b117-81a9dbd5365d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_d92561a1-d27f-4699-b117-81a9dbd5365d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_8404681b-62e7-46e3-91aa-53c59eedd345" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_8404681b-62e7-46e3-91aa-53c59eedd345" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_MaximumTermForDrawingLoanFacility_0f04dd9a-9a63-4a8f-8464-1f814246b039" xlink:href="notv-20240930.xsd#notv_MaximumTermForDrawingLoanFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_MaximumTermForDrawingLoanFacility_0f04dd9a-9a63-4a8f-8464-1f814246b039" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentNumberOfBusinessDaysFromEndOfEachMonthToPrepareCashFlowStatement_fd3bd3cb-ca7a-405a-909b-0ee5045ff611" xlink:href="notv-20240930.xsd#notv_DebtInstrumentNumberOfBusinessDaysFromEndOfEachMonthToPrepareCashFlowStatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentNumberOfBusinessDaysFromEndOfEachMonthToPrepareCashFlowStatement_fd3bd3cb-ca7a-405a-909b-0ee5045ff611" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantBudgetedPeriod_034b3c27-cf79-4746-8d92-aca207246760" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantBudgetedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantBudgetedPeriod_034b3c27-cf79-4746-8d92-aca207246760" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentAdjustmentRate_9acb48c2-b4ec-44f5-9880-3c06a61d029d" xlink:href="notv-20240930.xsd#notv_DebtInstrumentAdjustmentRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentAdjustmentRate_9acb48c2-b4ec-44f5-9880-3c06a61d029d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentVariableInterestFloorRate_93e3c783-b148-4990-93a4-a4c05a4420f6" xlink:href="notv-20240930.xsd#notv_DebtInstrumentVariableInterestFloorRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentVariableInterestFloorRate_93e3c783-b148-4990-93a4-a4c05a4420f6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_1325d580-872e-4e7c-ba0b-73b2e4d348e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_1325d580-872e-4e7c-ba0b-73b2e4d348e5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantFinancialAdvisorTerm_b1aed24a-2b82-47d4-b962-65113399daf5" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantFinancialAdvisorTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantFinancialAdvisorTerm_b1aed24a-2b82-47d4-b962-65113399daf5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DomesticCashAndCashEquivalentsOnHandAfterCreditFacilityDraw_3283707b-c885-4029-8233-6e4c11e79da6" xlink:href="notv-20240930.xsd#notv_DomesticCashAndCashEquivalentsOnHandAfterCreditFacilityDraw"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DomesticCashAndCashEquivalentsOnHandAfterCreditFacilityDraw_3283707b-c885-4029-8233-6e4c11e79da6" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentFeePercentScenarioOne_4902e901-aa1c-46dc-b361-2a273e466767" xlink:href="notv-20240930.xsd#notv_DebtInstrumentFeePercentScenarioOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentFeePercentScenarioOne_4902e901-aa1c-46dc-b361-2a273e466767" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentFeePercentScenarioTwo_975133bc-6d5e-494a-8ef1-7a4ba6d8ed20" xlink:href="notv-20240930.xsd#notv_DebtInstrumentFeePercentScenarioTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentFeePercentScenarioTwo_975133bc-6d5e-494a-8ef1-7a4ba6d8ed20" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentFeePercentScenarioThree_ad2f6728-cef6-409b-abdb-047394d6bc23" xlink:href="notv-20240930.xsd#notv_DebtInstrumentFeePercentScenarioThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentFeePercentScenarioThree_ad2f6728-cef6-409b-abdb-047394d6bc23" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantChargesOrExpensesAddbackLimit_cc271650-cfc8-4d38-a021-ed09cb92f256" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantChargesOrExpensesAddbackLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantChargesOrExpensesAddbackLimit_cc271650-cfc8-4d38-a021-ed09cb92f256" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_29742fd4-ee2c-4007-9376-5710eaf998b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_29742fd4-ee2c-4007-9376-5710eaf998b0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantWeeklyLiquidityRequirement_27033b64-7225-487e-acc4-aabe7128e3cf" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantWeeklyLiquidityRequirement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantWeeklyLiquidityRequirement_27033b64-7225-487e-acc4-aabe7128e3cf" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantCapOnFundsReinvestment_2ccccfad-b0b5-4653-b233-b0305f285af6" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantCapOnFundsReinvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantCapOnFundsReinvestment_2ccccfad-b0b5-4653-b233-b0305f285af6" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_1c1faece-fc31-4b43-801c-4cea010d9f3f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_1c1faece-fc31-4b43-801c-4cea010d9f3f" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentDebtDefaultCurePeriod_430742e5-5b28-4323-9fb4-ef4cd34987ac" xlink:href="notv-20240930.xsd#notv_DebtInstrumentDebtDefaultCurePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentDebtDefaultCurePeriod_430742e5-5b28-4323-9fb4-ef4cd34987ac" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantDefaultAmount_ee683c73-dd73-4c0c-99dc-ed6b87d8f26b" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantDefaultAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantDefaultAmount_ee683c73-dd73-4c0c-99dc-ed6b87d8f26b" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentWaiverPeriodAfterAcquisitionClosing_1889f298-b008-4b57-8f2d-f0feecb70575" xlink:href="notv-20240930.xsd#notv_DebtInstrumentWaiverPeriodAfterAcquisitionClosing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentWaiverPeriodAfterAcquisitionClosing_1889f298-b008-4b57-8f2d-f0feecb70575" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent_13273da1-db9d-4bc5-9f68-7da8cf32726b" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent_13273da1-db9d-4bc5-9f68-7da8cf32726b" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityExpirationPeriod_6b50a0f0-c795-4562-a33c-da540ae46628" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCreditFacilityExpirationPeriod_6b50a0f0-c795-4562-a33c-da540ae46628" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_75faf0fa-542d-4c59-ba65-73dee5c97e76" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f7fa6893-ab08-413a-a629-287b49372a12" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_75faf0fa-542d-4c59-ba65-73dee5c97e76" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTConvertibleSeniorNotesNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTConvertibleSeniorNotesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTConvertibleSeniorNotesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_414a09f0-7265-48e7-9e26-d45a6532ce7e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:to="loc_srt_CounterpartyNameAxis_414a09f0-7265-48e7-9e26-d45a6532ce7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_414a09f0-7265-48e7-9e26-d45a6532ce7e_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_414a09f0-7265-48e7-9e26-d45a6532ce7e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_414a09f0-7265-48e7-9e26-d45a6532ce7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_962e611d-87a4-4021-9ade-ca42e977824f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_414a09f0-7265-48e7-9e26-d45a6532ce7e" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_962e611d-87a4-4021-9ade-ca42e977824f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeventhAmendmentPurchasersMember_61be9342-27ed-477f-9c71-db5c7430068d" xlink:href="notv-20240930.xsd#notv_SeventhAmendmentPurchasersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_962e611d-87a4-4021-9ade-ca42e977824f" xlink:to="loc_notv_SeventhAmendmentPurchasersMember_61be9342-27ed-477f-9c71-db5c7430068d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:to="loc_us-gaap_DebtInstrumentAxis_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2e964d37-d4ff-4990-a083-6a5400752d21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_4d916aca-c08c-4a3a-b9ce-eb14bb5f746c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2e964d37-d4ff-4990-a083-6a5400752d21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleSeniorNotesMember_945bfb63-6f58-456e-88df-6216920321d9" xlink:href="notv-20240930.xsd#notv_ConvertibleSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2e964d37-d4ff-4990-a083-6a5400752d21" xlink:to="loc_notv_ConvertibleSeniorNotesMember_945bfb63-6f58-456e-88df-6216920321d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleSeniorNotesDue2027Member_4e668224-bd86-4c2f-89a0-6d09799d16c0" xlink:href="notv-20240930.xsd#notv_ConvertibleSeniorNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2e964d37-d4ff-4990-a083-6a5400752d21" xlink:to="loc_notv_ConvertibleSeniorNotesDue2027Member_4e668224-bd86-4c2f-89a0-6d09799d16c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_9ed806af-674b-4baa-b3c5-b817fb259604" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_9ed806af-674b-4baa-b3c5-b817fb259604" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_9ed806af-674b-4baa-b3c5-b817fb259604_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9ed806af-674b-4baa-b3c5-b817fb259604" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_9ed806af-674b-4baa-b3c5-b817fb259604_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_90133809-788b-4e4c-8fc2-8bbd94f4f549" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9ed806af-674b-4baa-b3c5-b817fb259604" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_90133809-788b-4e4c-8fc2-8bbd94f4f549" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_4512d08f-ed92-46a3-8018-1e4691a92748" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90133809-788b-4e4c-8fc2-8bbd94f4f549" xlink:to="loc_us-gaap_ConvertibleDebtMember_4512d08f-ed92-46a3-8018-1e4691a92748" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_eb0dbab3-513c-483b-8104-825c05208c38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a713c5f0-ff9d-4f4e-8da6-28f0fc95ffda" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_eb0dbab3-513c-483b-8104-825c05208c38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_eb0dbab3-513c-483b-8104-825c05208c38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_eb0dbab3-513c-483b-8104-825c05208c38" xlink:to="loc_us-gaap_TypeOfAdoptionMember_eb0dbab3-513c-483b-8104-825c05208c38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_272b8a39-eae6-4992-a1d0-763a79baf414" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_eb0dbab3-513c-483b-8104-825c05208c38" xlink:to="loc_us-gaap_TypeOfAdoptionMember_272b8a39-eae6-4992-a1d0-763a79baf414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate202006Member_3ea9b2d3-0f6b-4481-81c1-eaf90dfe3aaa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountingStandardsUpdate202006Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_272b8a39-eae6-4992-a1d0-763a79baf414" xlink:to="loc_us-gaap_AccountingStandardsUpdate202006Member_3ea9b2d3-0f6b-4481-81c1-eaf90dfe3aaa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_84f63399-c755-47bb-914d-455b2b34d0ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_84f63399-c755-47bb-914d-455b2b34d0ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_f334a88f-ec4a-462e-bf62-7030c1781b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_LongTermDebt_f334a88f-ec4a-462e-bf62-7030c1781b0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_151bb526-8a7a-4e8c-97c6-92c0ae998414" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_151bb526-8a7a-4e8c-97c6-92c0ae998414" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_a01e1523-9f03-4777-bdba-615dbc2f91e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_a01e1523-9f03-4777-bdba-615dbc2f91e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2aaa3615-a307-4a1b-b3c1-424103b7b10f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2aaa3615-a307-4a1b-b3c1-424103b7b10f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_1c469aeb-1e7b-4752-a36f-891a82f6feb7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_1c469aeb-1e7b-4752-a36f-891a82f6feb7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_11e88e3e-e2ef-497a-ab52-8d2071062564" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_11e88e3e-e2ef-497a-ab52-8d2071062564" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_3eff3048-1b2d-4ad2-9d0a-dae15b3deaf1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_InterestExpenseDebt_3eff3048-1b2d-4ad2-9d0a-dae15b3deaf1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_CouponInterestExpenseDebt_b3ff08d0-3367-44f9-a1ff-1a947ca10310" xlink:href="notv-20240930.xsd#notv_CouponInterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_CouponInterestExpenseDebt_b3ff08d0-3367-44f9-a1ff-1a947ca10310" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AccretionExpenseDebt_e3d43513-4757-4530-8db2-6202be271b77" xlink:href="notv-20240930.xsd#notv_AccretionExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_AccretionExpenseDebt_e3d43513-4757-4530-8db2-6202be271b77" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_43457112-7196-41dd-94ca-06dccfe65617" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_InterestAndDebtExpense_43457112-7196-41dd-94ca-06dccfe65617" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccretionExpense_0a59c291-401e-4fe9-89e7-e66cf1a8e5dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccretionExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_AccretionExpense_0a59c291-401e-4fe9-89e7-e66cf1a8e5dd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentDebtDefaultPeriodForDischargeOrStay_1965e7e6-a062-444c-bc11-71eb56cb5ee4" xlink:href="notv-20240930.xsd#notv_DebtInstrumentDebtDefaultPeriodForDischargeOrStay"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentDebtDefaultPeriodForDischargeOrStay_1965e7e6-a062-444c-bc11-71eb56cb5ee4" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentDebtDefaultNoticeForMinimumPercentageOfNoteholders_0511578d-68ac-41fd-880d-0b0ab6fa4ad4" xlink:href="notv-20240930.xsd#notv_DebtInstrumentDebtDefaultNoticeForMinimumPercentageOfNoteholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentDebtDefaultNoticeForMinimumPercentageOfNoteholders_0511578d-68ac-41fd-880d-0b0ab6fa4ad4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumTerm_d8e1cf48-7852-4c3c-b60c-9bc9d4078ee0" xlink:href="notv-20240930.xsd#notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumTerm_d8e1cf48-7852-4c3c-b60c-9bc9d4078ee0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumRate_b81a58c6-9b93-4a6c-8029-a94bd79fddd2" xlink:href="notv-20240930.xsd#notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentDebtDefaultRightToReceiveSpecialInterestMaximumRate_b81a58c6-9b93-4a6c-8029-a94bd79fddd2" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ConvertibleDebtFairValueRemeasurementOfEmbeddedDerivative_027e9b60-9b1e-4fd9-b0ea-14a7f112ec46" xlink:href="notv-20240930.xsd#notv_ConvertibleDebtFairValueRemeasurementOfEmbeddedDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_ConvertibleDebtFairValueRemeasurementOfEmbeddedDerivative_027e9b60-9b1e-4fd9-b0ea-14a7f112ec46" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent_cd97e382-e64c-4daa-8c6d-82e720f0d758" xlink:href="notv-20240930.xsd#notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentCovenantAggregateHoldersOfDebtPercent_cd97e382-e64c-4daa-8c6d-82e720f0d758" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_85d88247-7052-4def-a3c0-71d3c852d3de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_85d88247-7052-4def-a3c0-71d3c852d3de" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentSettlementTerm_cc39550d-8c47-42a1-841e-4b35ac2e4f9e" xlink:href="notv-20240930.xsd#notv_DebtInstrumentSettlementTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentSettlementTerm_cc39550d-8c47-42a1-841e-4b35ac2e4f9e" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DebtInstrumentAdditionalPrincipalAmountIssued_e0f3c126-6d20-4d93-be4b-7e5fbb318ac5" xlink:href="notv-20240930.xsd#notv_DebtInstrumentAdditionalPrincipalAmountIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2cc2dcaa-11de-4673-aabf-3d2d79c4d096" xlink:to="loc_notv_DebtInstrumentAdditionalPrincipalAmountIssued_e0f3c126-6d20-4d93-be4b-7e5fbb318ac5" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/DEBTAcquisitionRelatedDebtNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#DEBTAcquisitionRelatedDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/DEBTAcquisitionRelatedDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_57394909-a6fd-4c92-acc2-781c02028a0b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_8176675a-861e-4372-8785-ecd336b44c4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_57394909-a6fd-4c92-acc2-781c02028a0b" xlink:to="loc_us-gaap_DebtInstrumentTable_8176675a-861e-4372-8785-ecd336b44c4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_12ad7b00-de42-46b7-a569-5a512a6cb72e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_8176675a-861e-4372-8785-ecd336b44c4a" xlink:to="loc_us-gaap_DebtInstrumentAxis_12ad7b00-de42-46b7-a569-5a512a6cb72e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_12ad7b00-de42-46b7-a569-5a512a6cb72e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_12ad7b00-de42-46b7-a569-5a512a6cb72e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_12ad7b00-de42-46b7-a569-5a512a6cb72e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_12ad7b00-de42-46b7-a569-5a512a6cb72e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNotePreClinicalResearchServicesMember_01620e5e-ddbd-4858-a092-3c839372de00" xlink:href="notv-20240930.xsd#notv_SellerNotePreClinicalResearchServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNotePreClinicalResearchServicesMember_01620e5e-ddbd-4858-a092-3c839372de00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteBolderBiopathMember_fd33003c-a068-4ecc-b59a-33c4cb9d2584" xlink:href="notv-20240930.xsd#notv_SellerNoteBolderBiopathMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNoteBolderBiopathMember_fd33003c-a068-4ecc-b59a-33c4cb9d2584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNotePlatoBioPharmaIncMember_eb1ae004-0817-4d92-9dd6-7e24774d019e" xlink:href="notv-20240930.xsd#notv_SellerNotePlatoBioPharmaIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNotePlatoBioPharmaIncMember_eb1ae004-0817-4d92-9dd6-7e24774d019e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNotePlatoBiopharmaMember_877695e2-2256-4ccb-974d-b241dc718129" xlink:href="notv-20240930.xsd#notv_SellerNotePlatoBiopharmaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNotePlatoBiopharmaMember_877695e2-2256-4ccb-974d-b241dc718129" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteHistionMember_1052895b-a3ea-45d8-8b51-f74e8fbe3f61" xlink:href="notv-20240930.xsd#notv_SellerNoteHistionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNoteHistionMember_1052895b-a3ea-45d8-8b51-f74e8fbe3f61" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SellerNoteProtypiaMember_3e60b0d4-6237-4c2c-9c16-da4d0237a6ae" xlink:href="notv-20240930.xsd#notv_SellerNoteProtypiaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_508e891f-ab0d-4920-b83b-f1188e0bd194" xlink:to="loc_notv_SellerNoteProtypiaMember_3e60b0d4-6237-4c2c-9c16-da4d0237a6ae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a54be393-01c8-44f1-8ab0-171aef58d45a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_8176675a-861e-4372-8785-ecd336b44c4a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a54be393-01c8-44f1-8ab0-171aef58d45a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a54be393-01c8-44f1-8ab0-171aef58d45a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a54be393-01c8-44f1-8ab0-171aef58d45a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a54be393-01c8-44f1-8ab0-171aef58d45a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_78b15f4f-92ba-47bc-a5d6-8a81987188b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a54be393-01c8-44f1-8ab0-171aef58d45a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_78b15f4f-92ba-47bc-a5d6-8a81987188b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_9eb42801-9cfc-4d98-b478-f2cf7ad2c28b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_78b15f4f-92ba-47bc-a5d6-8a81987188b7" xlink:to="loc_us-gaap_UnsecuredDebtMember_9eb42801-9cfc-4d98-b478-f2cf7ad2c28b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_7dac253a-20b3-425d-b319-574c339c7f40" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_57394909-a6fd-4c92-acc2-781c02028a0b" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_7dac253a-20b3-425d-b319-574c339c7f40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_af5ca307-390a-4f3c-b398-05a8a745b703" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_57394909-a6fd-4c92-acc2-781c02028a0b" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_af5ca307-390a-4f3c-b398-05a8a745b703" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_994ab2ff-6c32-4f32-b3db-2d52fbfe2b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_57394909-a6fd-4c92-acc2-781c02028a0b" xlink:to="loc_us-gaap_LongTermDebtFairValue_994ab2ff-6c32-4f32-b3db-2d52fbfe2b9d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/SUPPLEMENTALBALANCESHEETINFORMATIONNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#SUPPLEMENTALBALANCESHEETINFORMATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/SUPPLEMENTALBALANCESHEETINFORMATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_notv_ScheduleOfTradeReceivablesAndContractAssetsNetLineItems_9d023f53-fc66-4721-a120-68980f9d8add" xlink:href="notv-20240930.xsd#notv_ScheduleOfTradeReceivablesAndContractAssetsNetLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_notv_ScheduleOfTradeReceivablesAndContractAssetsNetLineItems_9d023f53-fc66-4721-a120-68980f9d8add" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_08cacafb-6c97-4cd5-8248-482a4471a179" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_08cacafb-6c97-4cd5-8248-482a4471a179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08cacafb-6c97-4cd5-8248-482a4471a179_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_08cacafb-6c97-4cd5-8248-482a4471a179" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08cacafb-6c97-4cd5-8248-482a4471a179_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e225b49f-1fba-4223-b5f6-ebbf242ac011" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_08cacafb-6c97-4cd5-8248-482a4471a179" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e225b49f-1fba-4223-b5f6-ebbf242ac011" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeAccountsReceivableMember_34a617e8-a847-4adf-9090-62e0f65f2c1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TradeAccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e225b49f-1fba-4223-b5f6-ebbf242ac011" xlink:to="loc_us-gaap_TradeAccountsReceivableMember_34a617e8-a847-4adf-9090-62e0f65f2c1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_86130bde-5471-4a45-a8bc-0bc959a457ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_86130bde-5471-4a45-a8bc-0bc959a457ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_86130bde-5471-4a45-a8bc-0bc959a457ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_86130bde-5471-4a45-a8bc-0bc959a457ee" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_86130bde-5471-4a45-a8bc-0bc959a457ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_fcec2da6-599e-4edd-bd19-19681fe4a6ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_86130bde-5471-4a45-a8bc-0bc959a457ee" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_fcec2da6-599e-4edd-bd19-19681fe4a6ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_a4e31785-84f0-47b6-9a7b-b46ad54882b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_fcec2da6-599e-4edd-bd19-19681fe4a6ba" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_a4e31785-84f0-47b6-9a7b-b46ad54882b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1" xlink:to="loc_us-gaap_SegmentDomain_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_600e3333-e84e-462e-8329-1a130b98e835" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_eb2bc41f-bdd9-48a1-8665-b0f2c71388b1" xlink:to="loc_us-gaap_SegmentDomain_600e3333-e84e-462e-8329-1a130b98e835" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_8c1ea00f-d296-469f-a727-793ad47be19f" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_600e3333-e84e-462e-8329-1a130b98e835" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_8c1ea00f-d296-469f-a727-793ad47be19f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_f402c0db-29f4-448a-a626-057be40f3723" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_a2b102ac-1e99-4a05-899d-0c5be90d9cf7" xlink:to="loc_srt_MajorCustomersAxis_f402c0db-29f4-448a-a626-057be40f3723" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_f402c0db-29f4-448a-a626-057be40f3723_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_f402c0db-29f4-448a-a626-057be40f3723" xlink:to="loc_srt_NameOfMajorCustomerDomain_f402c0db-29f4-448a-a626-057be40f3723_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_008e7ec3-321d-4ede-9ec1-d57b761c9004" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_f402c0db-29f4-448a-a626-057be40f3723" xlink:to="loc_srt_NameOfMajorCustomerDomain_008e7ec3-321d-4ede-9ec1-d57b761c9004" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_OneCustomerMember_04c254b1-9b01-48f8-9934-abcb946d1785" xlink:href="notv-20240930.xsd#notv_OneCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_008e7ec3-321d-4ede-9ec1-d57b761c9004" xlink:to="loc_notv_OneCustomerMember_04c254b1-9b01-48f8-9934-abcb946d1785" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_25b14e09-dff9-4559-ae11-85152be3cc78" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_ScheduleOfTradeReceivablesAndContractAssetsNetLineItems_9d023f53-fc66-4721-a120-68980f9d8add" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_25b14e09-dff9-4559-ae11-85152be3cc78" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/SUPPLEMENTALBALANCESHEETINFORMATIONCompositionofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#SUPPLEMENTALBALANCESHEETINFORMATIONCompositionofPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/SUPPLEMENTALBALANCESHEETINFORMATIONCompositionofPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a2610ac1-7c93-422d-aa12-0f4ae923dc04" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_74d3f371-a2ee-4aa2-b0fa-8d6e7feb5da2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a2610ac1-7c93-422d-aa12-0f4ae923dc04" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_74d3f371-a2ee-4aa2-b0fa-8d6e7feb5da2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_74d3f371-a2ee-4aa2-b0fa-8d6e7feb5da2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4361cbcd-5fe6-4239-86f6-4a8d2ec310b5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAndLandImprovementsMember_9ee96465-0a44-4685-8f35-436cc4ee6fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LandAndLandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_LandAndLandImprovementsMember_9ee96465-0a44-4685-8f35-436cc4ee6fa6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_7833bcf4-bd8d-4fad-9298-5e6c7a09c246" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_7833bcf4-bd8d-4fad-9298-5e6c7a09c246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_31eebdf0-ef24-4368-b428-5e408ffe8247" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_31eebdf0-ef24-4368-b428-5e408ffe8247" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_a5d9fff3-51db-40b1-9183-babaab8e0201" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_a5d9fff3-51db-40b1-9183-babaab8e0201" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember_92b41352-c750-4b1f-a31f-840b3fbda397" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember_92b41352-c750-4b1f-a31f-840b3fbda397" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_e664cc0e-79e0-4719-879d-61ce34f937ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_419075e4-a3e2-4be2-b798-af9cb0bf5e70" xlink:to="loc_us-gaap_ConstructionInProgressMember_e664cc0e-79e0-4719-879d-61ce34f937ed" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_b732ec94-f3c0-425a-a4d6-7b1d1af0ad51" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a2610ac1-7c93-422d-aa12-0f4ae923dc04" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_b732ec94-f3c0-425a-a4d6-7b1d1af0ad51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_85b2c247-1c5f-4348-ad23-13dc824ff66d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a2610ac1-7c93-422d-aa12-0f4ae923dc04" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_85b2c247-1c5f-4348-ad23-13dc824ff66d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_ef836031-64c4-4056-a401-cd410653841d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a2610ac1-7c93-422d-aa12-0f4ae923dc04" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_ef836031-64c4-4056-a401-cd410653841d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/POSTEMPLOYMENTBENEFITSPlanassetsdistributionDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#POSTEMPLOYMENTBENEFITSPlanassetsdistributionDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/POSTEMPLOYMENTBENEFITSPlanassetsdistributionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_6dc5b5d2-e2cd-4d62-9fd5-1a91adeb2773" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_69bbfeb5-c23c-4f4f-95e2-19abf348f468" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_6dc5b5d2-e2cd-4d62-9fd5-1a91adeb2773" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_69bbfeb5-c23c-4f4f-95e2-19abf348f468" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_526cfe32-a4ee-4f92-9561-30d06fe9a3d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_69bbfeb5-c23c-4f4f-95e2-19abf348f468" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_526cfe32-a4ee-4f92-9561-30d06fe9a3d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_526cfe32-a4ee-4f92-9561-30d06fe9a3d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_526cfe32-a4ee-4f92-9561-30d06fe9a3d5" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_526cfe32-a4ee-4f92-9561-30d06fe9a3d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_526cfe32-a4ee-4f92-9561-30d06fe9a3d5" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashMember_dc99a853-26e9-4ea3-b04e-9fffc080947d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanCashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:to="loc_us-gaap_DefinedBenefitPlanCashMember_dc99a853-26e9-4ea3-b04e-9fffc080947d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_f68526ce-7e84-42e7-962b-fccb96312014" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_f68526ce-7e84-42e7-962b-fccb96312014" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_0f9fb921-ffea-44da-b489-2b4d4f60126c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanDebtSecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:to="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_0f9fb921-ffea-44da-b489-2b4d4f60126c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_3c77bb4c-bf97-4f60-9888-336b3d90de38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:to="loc_us-gaap_MutualFundMember_3c77bb4c-bf97-4f60-9888-336b3d90de38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DefinedBenefitPlanOtherMember_ea2f67a0-5117-4f5f-af00-3bda90efc2e7" xlink:href="notv-20240930.xsd#notv_DefinedBenefitPlanOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_b9f09dc4-daf0-40f1-b598-67ca07d2764f" xlink:to="loc_notv_DefinedBenefitPlanOtherMember_ea2f67a0-5117-4f5f-af00-3bda90efc2e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_7c0268dd-de0b-4f11-8229-15f32a48d9e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_6dc5b5d2-e2cd-4d62-9fd5-1a91adeb2773" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_7c0268dd-de0b-4f11-8229-15f32a48d9e2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/POSTEMPLOYMENTBENEFITSFairvalueoftotalplanassetsbyassetcategoryDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#POSTEMPLOYMENTBENEFITSFairvalueoftotalplanassetsbyassetcategoryDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/POSTEMPLOYMENTBENEFITSFairvalueoftotalplanassetsbyassetcategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryLineItems_4f456470-1fb8-4b6b-9850-d5e8b88e4ec4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanPlanAssetsCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryTable_46cbdc36-0676-440b-8962-ac98351bb08b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanPlanAssetsCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryLineItems_4f456470-1fb8-4b6b-9850-d5e8b88e4ec4" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryTable_46cbdc36-0676-440b-8962-ac98351bb08b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ee4c48a0-98ed-4944-889d-2d24e5d271de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryTable_46cbdc36-0676-440b-8962-ac98351bb08b" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ee4c48a0-98ed-4944-889d-2d24e5d271de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4c48a0-98ed-4944-889d-2d24e5d271de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ee4c48a0-98ed-4944-889d-2d24e5d271de" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ee4c48a0-98ed-4944-889d-2d24e5d271de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_15a0815d-4ba0-48cf-a8ab-842eb46daf5b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_ee4c48a0-98ed-4944-889d-2d24e5d271de" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_15a0815d-4ba0-48cf-a8ab-842eb46daf5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_18ba67a1-683d-45d0-aa7c-5d5eb7122058" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_15a0815d-4ba0-48cf-a8ab-842eb46daf5b" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_18ba67a1-683d-45d0-aa7c-5d5eb7122058" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_d1edc3ff-4c0b-44d5-8c93-37800fc890a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_15a0815d-4ba0-48cf-a8ab-842eb46daf5b" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_d1edc3ff-4c0b-44d5-8c93-37800fc890a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_bfc2a950-b94b-4312-9d11-9be9af580a53" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_15a0815d-4ba0-48cf-a8ab-842eb46daf5b" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_bfc2a950-b94b-4312-9d11-9be9af580a53" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9e5e84b5-8674-49cd-8157-2fdc4ff8586f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryTable_46cbdc36-0676-440b-8962-ac98351bb08b" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9e5e84b5-8674-49cd-8157-2fdc4ff8586f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_9e5e84b5-8674-49cd-8157-2fdc4ff8586f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9e5e84b5-8674-49cd-8157-2fdc4ff8586f" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_9e5e84b5-8674-49cd-8157-2fdc4ff8586f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_9e5e84b5-8674-49cd-8157-2fdc4ff8586f" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashMember_651f78cb-5c55-4738-8134-1e804d61c090" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanCashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:to="loc_us-gaap_DefinedBenefitPlanCashMember_651f78cb-5c55-4738-8134-1e804d61c090" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_40b32925-1aac-4154-83ae-215691f366d9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_40b32925-1aac-4154-83ae-215691f366d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_95355844-9dcf-4cf9-b914-addaa5eab42e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_95355844-9dcf-4cf9-b914-addaa5eab42e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DefinedBenefitPlanMultiAssetFundMember_13a134bb-3938-4fb8-becf-d0477e717e31" xlink:href="notv-20240930.xsd#notv_DefinedBenefitPlanMultiAssetFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_496efae0-c95a-4a0b-8aa8-15bb5c343f8b" xlink:to="loc_notv_DefinedBenefitPlanMultiAssetFundMember_13a134bb-3938-4fb8-becf-d0477e717e31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_2f9ba62a-00ac-43f9-9654-33a01d1ba862" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsCategoryLineItems_4f456470-1fb8-4b6b-9850-d5e8b88e4ec4" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_2f9ba62a-00ac-43f9-9654-33a01d1ba862" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/RESTRUCTURINGANDASSETSHELDFORSALEDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#RESTRUCTURINGANDASSETSHELDFORSALEDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/RESTRUCTURINGANDASSETSHELDFORSALEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_6111e887-6db9-4ede-8284-b966942649df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_us-gaap_RestructuringPlanAxis_6111e887-6db9-4ede-8284-b966942649df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_6111e887-6db9-4ede-8284-b966942649df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_6111e887-6db9-4ede-8284-b966942649df" xlink:to="loc_us-gaap_RestructuringPlanDomain_6111e887-6db9-4ede-8284-b966942649df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_fe3384b2-9544-46ea-8c4d-c836ed935752" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_6111e887-6db9-4ede-8284-b966942649df" xlink:to="loc_us-gaap_RestructuringPlanDomain_fe3384b2-9544-46ea-8c4d-c836ed935752" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SiteOptimizationPlanMember_4f9a4a96-6c4d-4e55-a4ab-d41bb2c4c3c0" xlink:href="notv-20240930.xsd#notv_SiteOptimizationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_fe3384b2-9544-46ea-8c4d-c836ed935752" xlink:to="loc_notv_SiteOptimizationPlanMember_4f9a4a96-6c4d-4e55-a4ab-d41bb2c4c3c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_ea30f2f6-9119-43ee-b278-bb854db56b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_ea30f2f6-9119-43ee-b278-bb854db56b7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_ea30f2f6-9119-43ee-b278-bb854db56b7e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ea30f2f6-9119-43ee-b278-bb854db56b7e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_ea30f2f6-9119-43ee-b278-bb854db56b7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_0d8eb4b2-776b-453d-9c47-45e6dcda2b39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ea30f2f6-9119-43ee-b278-bb854db56b7e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_0d8eb4b2-776b-453d-9c47-45e6dcda2b39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_e3962131-8b7f-4039-b89b-45ceef795907" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_0d8eb4b2-776b-453d-9c47-45e6dcda2b39" xlink:to="loc_us-gaap_EmployeeSeveranceMember_e3962131-8b7f-4039-b89b-45ceef795907" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_2fa721e9-b69e-4aa9-bb34-38928ef5920d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_0d8eb4b2-776b-453d-9c47-45e6dcda2b39" xlink:to="loc_us-gaap_OtherRestructuringMember_2fa721e9-b69e-4aa9-bb34-38928ef5920d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5" xlink:to="loc_us-gaap_SegmentDomain_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_04ee3b74-96b1-401d-8a3c-62a31377fbe3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d6e6b97e-e0d3-4f7d-b6a6-1c38cb6945c5" xlink:to="loc_us-gaap_SegmentDomain_04ee3b74-96b1-401d-8a3c-62a31377fbe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_b5ac2a84-fb58-46a2-b5ae-5d8f49dd3671" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_04ee3b74-96b1-401d-8a3c-62a31377fbe3" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_b5ac2a84-fb58-46a2-b5ae-5d8f49dd3671" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_41e6b184-21ed-4e98-96cc-949e0e591e69" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_srt_OwnershipAxis_41e6b184-21ed-4e98-96cc-949e0e591e69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_41e6b184-21ed-4e98-96cc-949e0e591e69_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_41e6b184-21ed-4e98-96cc-949e0e591e69" xlink:to="loc_srt_OwnershipDomain_41e6b184-21ed-4e98-96cc-949e0e591e69_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_2f32cc2d-2d3b-4761-8f57-2bcd758d9bfa" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_41e6b184-21ed-4e98-96cc-949e0e591e69" xlink:to="loc_srt_OwnershipDomain_2f32cc2d-2d3b-4761-8f57-2bcd758d9bfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_IsraelCRSMember_c03e5651-36c7-4386-9087-719069f460f8" xlink:href="notv-20240930.xsd#notv_IsraelCRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_2f32cc2d-2d3b-4761-8f57-2bcd758d9bfa" xlink:to="loc_notv_IsraelCRSMember_c03e5651-36c7-4386-9087-719069f460f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_cbbd1ba3-5a9e-4179-a358-043f5666a562" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_cbbd1ba3-5a9e-4179-a358-043f5666a562" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_cbbd1ba3-5a9e-4179-a358-043f5666a562_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_cbbd1ba3-5a9e-4179-a358-043f5666a562" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_cbbd1ba3-5a9e-4179-a358-043f5666a562_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_6a4aca79-57b7-4c99-9027-92c2b0efeefe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_cbbd1ba3-5a9e-4179-a358-043f5666a562" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_6a4aca79-57b7-4c99-9027-92c2b0efeefe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_8d946839-8f5a-4463-9c9b-7f8348e3ebb0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_6a4aca79-57b7-4c99-9027-92c2b0efeefe" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_8d946839-8f5a-4463-9c9b-7f8348e3ebb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5ff397bb-199d-4d6a-8221-0b496d80375a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4484dda5-07ca-4fe2-8f46-c84bdd8a58f3" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5ff397bb-199d-4d6a-8221-0b496d80375a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_IsraelRmsAndIsraelCrsBusinessesMember_23012484-ae2a-4521-a0b0-b177f42b46be" xlink:href="notv-20240930.xsd#notv_IsraelRmsAndIsraelCrsBusinessesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5ff397bb-199d-4d6a-8221-0b496d80375a" xlink:to="loc_notv_IsraelRmsAndIsraelCrsBusinessesMember_23012484-ae2a-4521-a0b0-b177f42b46be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a5c08a6f-909f-4fc3-98c6-82f6634197f3" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_8477e778-6e60-471a-997e-5eb8e1f7575f" xlink:to="loc_dei_LegalEntityAxis_a5c08a6f-909f-4fc3-98c6-82f6634197f3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a5c08a6f-909f-4fc3-98c6-82f6634197f3_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a5c08a6f-909f-4fc3-98c6-82f6634197f3" xlink:to="loc_dei_EntityDomain_a5c08a6f-909f-4fc3-98c6-82f6634197f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_86b7340e-8bc2-4851-bb9f-e182e6e78fde" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a5c08a6f-909f-4fc3-98c6-82f6634197f3" xlink:to="loc_dei_EntityDomain_86b7340e-8bc2-4851-bb9f-e182e6e78fde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_IsraelRmsMember_3af69155-593d-4f4b-a16b-cac454632026" xlink:href="notv-20240930.xsd#notv_IsraelRmsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_86b7340e-8bc2-4851-bb9f-e182e6e78fde" xlink:to="loc_notv_IsraelRmsMember_3af69155-593d-4f4b-a16b-cac454632026" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_ef41409d-9c3a-479c-b8a9-9eefb861a0d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringAndRelatedCostCostIncurredToDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_ef41409d-9c3a-479c-b8a9-9eefb861a0d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_ffc9136f-b5c3-4dc8-a0f7-de47a0a323a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_PaymentsForRestructuring_ffc9136f-b5c3-4dc8-a0f7-de47a0a323a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_d5ce894f-26a7-4dcd-91a9-9880df7bbcd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_RestructuringReserve_d5ce894f-26a7-4dcd-91a9-9880df7bbcd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_88f18965-146c-4798-9251-104fbe230182" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_AssetImpairmentCharges_88f18965-146c-4798-9251-104fbe230182" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCash_854dd142-d8f2-4f79-8e34-c041c2f883d2" xlink:href="notv-20240930.xsd#notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCash_854dd142-d8f2-4f79-8e34-c041c2f883d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCashAdjustment_a5ba2bf8-ae73-4e47-a6c8-5747fcf08efa" xlink:href="notv-20240930.xsd#notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCashAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationCashAdjustment_a5ba2bf8-ae73-4e47-a6c8-5747fcf08efa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationRealProperty_d451cc22-3006-48b0-a1d0-64011e8524a4" xlink:href="notv-20240930.xsd#notv_DisposalGroupIncludingDiscontinuedOperationConsiderationRealProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationRealProperty_d451cc22-3006-48b0-a1d0-64011e8524a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationPromissoryNoteReceivable_c2cd1adc-3174-4381-a205-e2dea8ce3bba" xlink:href="notv-20240930.xsd#notv_DisposalGroupIncludingDiscontinuedOperationConsiderationPromissoryNoteReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_DisposalGroupIncludingDiscontinuedOperationConsiderationPromissoryNoteReceivable_c2cd1adc-3174-4381-a205-e2dea8ce3bba" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_DisposalGroupIncludingDiscontinuedOperationNoteReceivableStatedInterestRate_68283b92-2ef2-470b-a8ae-8dc022123e2c" xlink:href="notv-20240930.xsd#notv_DisposalGroupIncludingDiscontinuedOperationNoteReceivableStatedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_DisposalGroupIncludingDiscontinuedOperationNoteReceivableStatedInterestRate_68283b92-2ef2-470b-a8ae-8dc022123e2c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_PercentageOfInterestSold_5316aef0-5e99-47bc-b64f-254d297ab6a2" xlink:href="notv-20240930.xsd#notv_PercentageOfInterestSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_notv_PercentageOfInterestSold_5316aef0-5e99-47bc-b64f-254d297ab6a2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_715b2e84-976b-4009-be29-bc69c18ad302" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_715b2e84-976b-4009-be29-bc69c18ad302" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_d84a7648-cb5d-4324-8466-36a775da71b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_d84a7648-cb5d-4324-8466-36a775da71b1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposalStatementOfIncomeExtensibleList_34b1e1ac-386a-4840-b761-c175ec0945e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposalStatementOfIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposalStatementOfIncomeExtensibleList_34b1e1ac-386a-4840-b761-c175ec0945e4" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_462882d5-b325-478f-b5a3-c69c349d3884" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_25bc032e-63fa-4c73-9762-72eecf3b5671" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_462882d5-b325-478f-b5a3-c69c349d3884" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKHOLDERSEQUITYANDLOSSPERSHARENarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKHOLDERSEQUITYANDLOSSPERSHARENarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKHOLDERSEQUITYANDLOSSPERSHARENarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:href="notv-20240930.xsd#notv_StockAndWarrantsByClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_abcb6c72-b2d6-4fc4-b4cd-0cc0214e1c1c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_abcb6c72-b2d6-4fc4-b4cd-0cc0214e1c1c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_49d825e6-e3c1-4e7b-b892-2a076c353ff8" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_abcb6c72-b2d6-4fc4-b4cd-0cc0214e1c1c" xlink:to="loc_srt_CounterpartyNameAxis_49d825e6-e3c1-4e7b-b892-2a076c353ff8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_49d825e6-e3c1-4e7b-b892-2a076c353ff8_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_49d825e6-e3c1-4e7b-b892-2a076c353ff8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_49d825e6-e3c1-4e7b-b892-2a076c353ff8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_5eae74e0-5a57-4950-a2cd-f7a70f9bc7cb" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_49d825e6-e3c1-4e7b-b892-2a076c353ff8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_5eae74e0-5a57-4950-a2cd-f7a70f9bc7cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_SeventhAmendmentStructuringAgentMember_0c38561d-dd1f-43c0-81d7-3465f5d95610" xlink:href="notv-20240930.xsd#notv_SeventhAmendmentStructuringAgentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_5eae74e0-5a57-4950-a2cd-f7a70f9bc7cb" xlink:to="loc_notv_SeventhAmendmentStructuringAgentMember_0c38561d-dd1f-43c0-81d7-3465f5d95610" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_0d8724d7-1d82-4925-8f0e-46acf6f96d56" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_abcb6c72-b2d6-4fc4-b4cd-0cc0214e1c1c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_0d8724d7-1d82-4925-8f0e-46acf6f96d56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0d8724d7-1d82-4925-8f0e-46acf6f96d56_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0d8724d7-1d82-4925-8f0e-46acf6f96d56" xlink:to="loc_us-gaap_ClassOfStockDomain_0d8724d7-1d82-4925-8f0e-46acf6f96d56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e0848b64-7fe4-46ff-a1d3-a7ed6b9ce68b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0d8724d7-1d82-4925-8f0e-46acf6f96d56" xlink:to="loc_us-gaap_ClassOfStockDomain_e0848b64-7fe4-46ff-a1d3-a7ed6b9ce68b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_43a1c918-456b-46af-9d04-3c4d7e24eadf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e0848b64-7fe4-46ff-a1d3-a7ed6b9ce68b" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_43a1c918-456b-46af-9d04-3c4d7e24eadf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_929da36a-2dbc-4c61-851d-6854ea1b847a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_abcb6c72-b2d6-4fc4-b4cd-0cc0214e1c1c" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_929da36a-2dbc-4c61-851d-6854ea1b847a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_929da36a-2dbc-4c61-851d-6854ea1b847a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_929da36a-2dbc-4c61-851d-6854ea1b847a" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_929da36a-2dbc-4c61-851d-6854ea1b847a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_929da36a-2dbc-4c61-851d-6854ea1b847a" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_0444c7f4-89a5-460b-b896-b967508d1208" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_0444c7f4-89a5-460b-b896-b967508d1208" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_be2f8d65-80be-4a10-adb8-1c566ae70b66" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_be2f8d65-80be-4a10-adb8-1c566ae70b66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_087da799-f2d4-4dee-a469-bc229300f856" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_087da799-f2d4-4dee-a469-bc229300f856" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_f1a76620-894c-450b-aabe-089e7a7082de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_dc0f5a42-3b49-4c5e-9497-321498d8a650" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_f1a76620-894c-450b-aabe-089e7a7082de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_ab8f0365-9188-4465-893d-bb0205e7744b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_ab8f0365-9188-4465-893d-bb0205e7744b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_5f4b7f09-98bc-42d8-965e-b01b6e211228" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_5f4b7f09-98bc-42d8-965e-b01b6e211228" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_b3a85613-d5c2-4670-8218-6ab99b88fd17" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_b3a85613-d5c2-4670-8218-6ab99b88fd17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_59308e94-69d9-44a9-b441-89a0132f727b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_59308e94-69d9-44a9-b441-89a0132f727b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_CommonAndPreferredStockSharesAuthorized_2f07e580-239b-4167-833b-f9114fa22f02" xlink:href="notv-20240930.xsd#notv_CommonAndPreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_notv_CommonAndPreferredStockSharesAuthorized_2f07e580-239b-4167-833b-f9114fa22f02" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_bc5f38d2-83dd-4a5d-a68c-03cc9f5cc22e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_bc5f38d2-83dd-4a5d-a68c-03cc9f5cc22e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_13acb98c-9242-4b72-b822-3778c1bb7d2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_13acb98c-9242-4b72-b822-3778c1bb7d2d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_1f2187d3-f78c-4e94-a0c0-1a8bae2b8c54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_1f2187d3-f78c-4e94-a0c0-1a8bae2b8c54" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_ff1f900c-0d89-49fa-845f-85bc87505532" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_StockAndWarrantsByClassLineItems_bc537269-4103-4589-82e6-c0d91467fa54" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_ff1f900c-0d89-49fa-845f-85bc87505532" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKHOLDERSEQUITYANDLOSSPERSHAREBasicanddilutednetlossincomepershareDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKHOLDERSEQUITYANDLOSSPERSHAREBasicanddilutednetlossincomepershareDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKHOLDERSEQUITYANDLOSSPERSHAREBasicanddilutednetlossincomepershareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b7eb8bc3-dc4f-4e15-8474-e8df3a1aaa0f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3655d5e0-4756-4ddb-9b46-96ef9068bbe6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b7eb8bc3-dc4f-4e15-8474-e8df3a1aaa0f" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3655d5e0-4756-4ddb-9b46-96ef9068bbe6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_71fc5e6e-fb10-44dc-92ea-c3a0a467514f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_3655d5e0-4756-4ddb-9b46-96ef9068bbe6" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_71fc5e6e-fb10-44dc-92ea-c3a0a467514f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_71fc5e6e-fb10-44dc-92ea-c3a0a467514f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_71fc5e6e-fb10-44dc-92ea-c3a0a467514f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_71fc5e6e-fb10-44dc-92ea-c3a0a467514f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae6bae7a-9b1f-40a9-8b03-8735017a5dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_71fc5e6e-fb10-44dc-92ea-c3a0a467514f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae6bae7a-9b1f-40a9-8b03-8735017a5dc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_57f44ce6-29f4-47e4-9f26-14959f0c4b11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae6bae7a-9b1f-40a9-8b03-8735017a5dc5" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_57f44ce6-29f4-47e4-9f26-14959f0c4b11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_17448294-a256-4263-8d29-510fbbf1f6ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae6bae7a-9b1f-40a9-8b03-8735017a5dc5" xlink:to="loc_us-gaap_WarrantMember_17448294-a256-4263-8d29-510fbbf1f6ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_247fda8b-c357-43eb-8101-046789c67cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b7eb8bc3-dc4f-4e15-8474-e8df3a1aaa0f" xlink:to="loc_us-gaap_EarningsPerShareAbstract_247fda8b-c357-43eb-8101-046789c67cb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_7aebbc86-1d78-417d-bfa5-e16d7671d3d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_247fda8b-c357-43eb-8101-046789c67cb5" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_7aebbc86-1d78-417d-bfa5-e16d7671d3d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_736a36ca-5668-4e83-84bf-48f00583df9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_7aebbc86-1d78-417d-bfa5-e16d7671d3d4" xlink:to="loc_us-gaap_ProfitLoss_736a36ca-5668-4e83-84bf-48f00583df9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_ed236d92-dc71-4b21-b482-fb35702cb78a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_7aebbc86-1d78-417d-bfa5-e16d7671d3d4" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_ed236d92-dc71-4b21-b482-fb35702cb78a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_087bb792-aac7-43a1-ac0f-2faa1d61599a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDilutedAbstract_7aebbc86-1d78-417d-bfa5-e16d7671d3d4" xlink:to="loc_us-gaap_NetIncomeLoss_087bb792-aac7-43a1-ac0f-2faa1d61599a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_c7d79cda-2621-47bd-8cd3-b42e4db099c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_247fda8b-c357-43eb-8101-046789c67cb5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_c7d79cda-2621-47bd-8cd3-b42e4db099c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e5931e02-4f92-4f79-9122-641fed4925e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_c7d79cda-2621-47bd-8cd3-b42e4db099c5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e5931e02-4f92-4f79-9122-641fed4925e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_764276aa-78c6-4e25-9490-402575663f72" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_c7d79cda-2621-47bd-8cd3-b42e4db099c5" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_764276aa-78c6-4e25-9490-402575663f72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b57160d6-e36c-4320-ad0f-bdc2c4904211" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_c7d79cda-2621-47bd-8cd3-b42e4db099c5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b57160d6-e36c-4320-ad0f-bdc2c4904211" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:to="loc_us-gaap_AwardTypeAxis_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f4959667-f8de-4d1a-8068-5efa3fe73d45" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e8fb7a3c-431e-4127-9aa3-0e6084b6c2b4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f4959667-f8de-4d1a-8068-5efa3fe73d45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_1e906c2f-7f39-4159-aa30-cc6adea640a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f4959667-f8de-4d1a-8068-5efa3fe73d45" xlink:to="loc_us-gaap_EmployeeStockOptionMember_1e906c2f-7f39-4159-aa30-cc6adea640a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_de6597cc-e3e8-4d29-ab56-5735c2b03373" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f4959667-f8de-4d1a-8068-5efa3fe73d45" xlink:to="loc_us-gaap_RestrictedStockMember_de6597cc-e3e8-4d29-ab56-5735c2b03373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_895f9996-907f-45df-a075-35279b750962" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f4959667-f8de-4d1a-8068-5efa3fe73d45" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_895f9996-907f-45df-a075-35279b750962" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_92d7c8c3-e1c7-404a-b2ab-d4c730c446df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:to="loc_us-gaap_PlanNameAxis_92d7c8c3-e1c7-404a-b2ab-d4c730c446df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_92d7c8c3-e1c7-404a-b2ab-d4c730c446df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_92d7c8c3-e1c7-404a-b2ab-d4c730c446df" xlink:to="loc_us-gaap_PlanNameDomain_92d7c8c3-e1c7-404a-b2ab-d4c730c446df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_5554db67-a59b-41b7-b74c-a809598faf6e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_92d7c8c3-e1c7-404a-b2ab-d4c730c446df" xlink:to="loc_us-gaap_PlanNameDomain_5554db67-a59b-41b7-b74c-a809598faf6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TwoThousandEighteenEquityIncentivePlanMember_0c78fbc0-b2f0-4cc1-ba35-be3d7fabb539" xlink:href="notv-20240930.xsd#notv_TwoThousandEighteenEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5554db67-a59b-41b7-b74c-a809598faf6e" xlink:to="loc_notv_TwoThousandEighteenEquityIncentivePlanMember_0c78fbc0-b2f0-4cc1-ba35-be3d7fabb539" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_TwoThousandTwentyOneEquityIncentivePlanMember_21422923-f629-4441-8ae1-f3eedbeb7ef1" xlink:href="notv-20240930.xsd#notv_TwoThousandTwentyOneEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5554db67-a59b-41b7-b74c-a809598faf6e" xlink:to="loc_notv_TwoThousandTwentyOneEquityIncentivePlanMember_21422923-f629-4441-8ae1-f3eedbeb7ef1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_700174f9-66ee-4342-8b05-aceb55465f7a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_700174f9-66ee-4342-8b05-aceb55465f7a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_700174f9-66ee-4342-8b05-aceb55465f7a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_700174f9-66ee-4342-8b05-aceb55465f7a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_700174f9-66ee-4342-8b05-aceb55465f7a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1b753470-f6a5-49c0-8039-bfe56167b4a3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_700174f9-66ee-4342-8b05-aceb55465f7a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1b753470-f6a5-49c0-8039-bfe56167b4a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_EnvigoMember_6d2395b8-5f5c-48e3-bb8e-fe03cc519484" xlink:href="notv-20240930.xsd#notv_EnvigoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1b753470-f6a5-49c0-8039-bfe56167b4a3" xlink:to="loc_notv_EnvigoMember_6d2395b8-5f5c-48e3-bb8e-fe03cc519484" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_c8296f9a-ad57-4b03-91fe-2388a496e661" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_87d08f87-2adb-4fa0-bffc-0f0a24e3d18a" xlink:to="loc_srt_RangeAxis_c8296f9a-ad57-4b03-91fe-2388a496e661" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c8296f9a-ad57-4b03-91fe-2388a496e661_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_c8296f9a-ad57-4b03-91fe-2388a496e661" xlink:to="loc_srt_RangeMember_c8296f9a-ad57-4b03-91fe-2388a496e661_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_46bc7ba6-3380-485f-a1d5-88b19e80e9c2" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_c8296f9a-ad57-4b03-91fe-2388a496e661" xlink:to="loc_srt_RangeMember_46bc7ba6-3380-485f-a1d5-88b19e80e9c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f26a4e9e-3b5d-40b1-a4f6-d2a772b00372" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_46bc7ba6-3380-485f-a1d5-88b19e80e9c2" xlink:to="loc_srt_MinimumMember_f26a4e9e-3b5d-40b1-a4f6-d2a772b00372" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_7793b564-5e16-48b5-b056-05844ff15ae5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_46bc7ba6-3380-485f-a1d5-88b19e80e9c2" xlink:to="loc_srt_MaximumMember_7793b564-5e16-48b5-b056-05844ff15ae5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_4da8ad2b-fd85-41df-9ba9-f2919e717337" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_4da8ad2b-fd85-41df-9ba9-f2919e717337" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_c7765168-d29a-4644-8fae-f7ba52c26eb9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_c7765168-d29a-4644-8fae-f7ba52c26eb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodPostTermination_3b120534-2d35-4083-bc27-9b182d3b8dbb" xlink:href="notv-20240930.xsd#notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodPostTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodPostTermination_3b120534-2d35-4083-bc27-9b182d3b8dbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_f15beefd-43aa-47a0-bee8-56b077609e51" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_f15beefd-43aa-47a0-bee8-56b077609e51" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_92babd05-8b30-4860-be15-c31f8594cef3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_92babd05-8b30-4860-be15-c31f8594cef3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_bdd497bc-91ed-46c6-bf31-0ebee45a5090" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_bdd497bc-91ed-46c6-bf31-0ebee45a5090" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_a6fc405d-e53d-4286-8c6b-a8b48ae248e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_a6fc405d-e53d-4286-8c6b-a8b48ae248e4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_63aad077-1755-4689-9b48-0b9e216db354" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_63aad077-1755-4689-9b48-0b9e216db354" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_450687ee-8f5d-4a9d-bd87-9ed1568eb9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_450687ee-8f5d-4a9d-bd87-9ed1568eb9e8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_5051e1e0-0bd1-4a14-9501-3f4c716d21a0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_5051e1e0-0bd1-4a14-9501-3f4c716d21a0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_782e50ab-11fa-4433-940f-b282c6aaf926" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_782e50ab-11fa-4433-940f-b282c6aaf926" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodFairValue_02cd0ef4-f6ee-4f8f-b489-3872e643c79f" xlink:href="notv-20240930.xsd#notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodFairValue_02cd0ef4-f6ee-4f8f-b489-3872e643c79f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_640bac1d-39da-4cd6-a20d-3d48e88c6b77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b6ea0c86-0762-443a-b414-d96c8b1ad72a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_640bac1d-39da-4cd6-a20d-3d48e88c6b77" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKBASEDCOMPENSATIONStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5e364476-9095-403d-a727-85a0d3bbeaca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_33a84287-e7bc-4ece-8e1e-ed0f73df7ec0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5e364476-9095-403d-a727-85a0d3bbeaca" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_33a84287-e7bc-4ece-8e1e-ed0f73df7ec0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_77442cad-e3e2-4912-8d25-af729b4cc9e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_33a84287-e7bc-4ece-8e1e-ed0f73df7ec0" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_77442cad-e3e2-4912-8d25-af729b4cc9e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_77442cad-e3e2-4912-8d25-af729b4cc9e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_77442cad-e3e2-4912-8d25-af729b4cc9e9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_77442cad-e3e2-4912-8d25-af729b4cc9e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_49e69528-0b19-4896-a796-b95b1ddf2bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_77442cad-e3e2-4912-8d25-af729b4cc9e9" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_49e69528-0b19-4896-a796-b95b1ddf2bdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_89d93fdb-8768-47f7-b6b9-be2434ee225e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_49e69528-0b19-4896-a796-b95b1ddf2bdf" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_89d93fdb-8768-47f7-b6b9-be2434ee225e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenseMember_ebbfbd64-f86f-4823-ab74-a2ff51691cfb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_49e69528-0b19-4896-a796-b95b1ddf2bdf" xlink:to="loc_us-gaap_OtherExpenseMember_ebbfbd64-f86f-4823-ab74-a2ff51691cfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_07788f56-b75c-477a-a78a-fa5b5fb782fd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5e364476-9095-403d-a727-85a0d3bbeaca" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_07788f56-b75c-477a-a78a-fa5b5fb782fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_09e02840-34cb-4c1b-afa3-ebc872e771a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5e364476-9095-403d-a727-85a0d3bbeaca" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_09e02840-34cb-4c1b-afa3-ebc872e771a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax_c46f4794-331c-48c0-ae3e-8dd54eb0b151" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5e364476-9095-403d-a727-85a0d3bbeaca" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax_c46f4794-331c-48c0-ae3e-8dd54eb0b151" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONStockOptionActivityDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKBASEDCOMPENSATIONStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONStockOptionActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_af41b313-33aa-4311-af6f-0844e4772147" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_af41b313-33aa-4311-af6f-0844e4772147" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_af41b313-33aa-4311-af6f-0844e4772147" xlink:to="loc_us-gaap_AwardTypeAxis_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_bc546df4-8274-41e2-9ffe-ff71acfc1dbb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_fd0ef04c-1ff2-4dae-b8ae-c99125e45f85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_bc546df4-8274-41e2-9ffe-ff71acfc1dbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_16345a58-8bd8-4bd1-95f0-702974b61e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_bc546df4-8274-41e2-9ffe-ff71acfc1dbb" xlink:to="loc_us-gaap_EmployeeStockOptionMember_16345a58-8bd8-4bd1-95f0-702974b61e3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2f6534d8-beaa-4fbf-a0b0-c3d583410283" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2f6534d8-beaa-4fbf-a0b0-c3d583410283" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_7d65f9b7-d56b-4d2d-958e-359ac8865d55" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_7d65f9b7-d56b-4d2d-958e-359ac8865d55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_db3e0d8d-58a1-415c-9c78-a16276368541" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_db3e0d8d-58a1-415c-9c78-a16276368541" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_4d9f95e8-1f39-471b-a774-8f6318ef6086" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_0e230b22-3a00-4e3f-9a87-12d01cea9f9e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_4d9f95e8-1f39-471b-a774-8f6318ef6086" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_c2241dc9-1ebc-4a44-b97c-30ea7019d009" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_6d3dbc42-bb75-480f-b04b-7df51f16e06d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_6d3dbc42-bb75-480f-b04b-7df51f16e06d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_5dd18e3f-69fa-43de-bd43-8d9a555e55bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_5dd18e3f-69fa-43de-bd43-8d9a555e55bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_4794efd5-a269-499d-95b3-a94ac268d9be" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_4794efd5-a269-499d-95b3-a94ac268d9be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_988e1808-a8f8-417e-a0b9-96b2f743c33e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_988e1808-a8f8-417e-a0b9-96b2f743c33e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_2efc1c69-1ae5-4105-b3f5-133e741316ab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_2efc1c69-1ae5-4105-b3f5-133e741316ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_2a92d410-f6d9-4a68-a25f-8ff484a3a6ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_7f19f17c-fab2-4999-be62-6d97e4504b56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_2a92d410-f6d9-4a68-a25f-8ff484a3a6ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_48391dfe-ae0d-4c9b-a37c-894085f5fc33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_ed27c09a-03f3-436c-a16b-fb036eeec588" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_ed27c09a-03f3-436c-a16b-fb036eeec588" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_c0311727-2a42-4b3a-9b5b-be1116d5fcc1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_c0311727-2a42-4b3a-9b5b-be1116d5fcc1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_342bdb4b-8960-4970-9e1a-f4bc3b953388" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_342bdb4b-8960-4970-9e1a-f4bc3b953388" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_dfa63e0d-7a86-49fc-b0b1-0620e7dae8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_342bdb4b-8960-4970-9e1a-f4bc3b953388" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_dfa63e0d-7a86-49fc-b0b1-0620e7dae8e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_802586eb-f2f9-45d4-bc1c-e8abb5dac708" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_342bdb4b-8960-4970-9e1a-f4bc3b953388" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_802586eb-f2f9-45d4-bc1c-e8abb5dac708" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_262752d8-c752-4ba6-9e15-f9bcb10d7e86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_342bdb4b-8960-4970-9e1a-f4bc3b953388" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_262752d8-c752-4ba6-9e15-f9bcb10d7e86" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract_a7d714a8-701c-4aed-b1eb-eb4394254d30" xlink:href="notv-20240930.xsd#notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e608e420-a485-4649-b036-2d65034983cc" xlink:to="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract_a7d714a8-701c-4aed-b1eb-eb4394254d30" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_d6b9eb3e-311b-434c-8b17-f4b164a6d278" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract_a7d714a8-701c-4aed-b1eb-eb4394254d30" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_d6b9eb3e-311b-434c-8b17-f4b164a6d278" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_07d2a4ec-6051-4127-95cc-79ecae4d39b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract_a7d714a8-701c-4aed-b1eb-eb4394254d30" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_07d2a4ec-6051-4127-95cc-79ecae4d39b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_64ce12aa-f556-481c-9545-eb7ce8ff930c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueAbstract_a7d714a8-701c-4aed-b1eb-eb4394254d30" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_64ce12aa-f556-481c-9545-eb7ce8ff930c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONRestrictedSharesandRestrictedStockUnitsActivityDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#STOCKBASEDCOMPENSATIONRestrictedSharesandRestrictedStockUnitsActivityDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/STOCKBASEDCOMPENSATIONRestrictedSharesandRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6388194b-08a0-4c44-91c8-31f841e30caf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_26ad1c98-a065-4242-892b-5e4dab12264b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6388194b-08a0-4c44-91c8-31f841e30caf" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_26ad1c98-a065-4242-892b-5e4dab12264b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d48976ec-1fde-4229-8b87-fe58df739c15" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_26ad1c98-a065-4242-892b-5e4dab12264b" xlink:to="loc_us-gaap_AwardTypeAxis_d48976ec-1fde-4229-8b87-fe58df739c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d48976ec-1fde-4229-8b87-fe58df739c15_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d48976ec-1fde-4229-8b87-fe58df739c15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d48976ec-1fde-4229-8b87-fe58df739c15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b9fb80e2-2c75-428f-8975-e990955081f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d48976ec-1fde-4229-8b87-fe58df739c15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b9fb80e2-2c75-428f-8975-e990955081f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_7a80ceca-737e-427e-b846-7bc95916250b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b9fb80e2-2c75-428f-8975-e990955081f5" xlink:to="loc_us-gaap_RestrictedStockMember_7a80ceca-737e-427e-b846-7bc95916250b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_4607d9b0-c26f-4959-b29b-939e6c20c7a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b9fb80e2-2c75-428f-8975-e990955081f5" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_4607d9b0-c26f-4959-b29b-939e6c20c7a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6388194b-08a0-4c44-91c8-31f841e30caf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_17da5982-f0a8-492b-8040-30f4a62e2ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_17da5982-f0a8-492b-8040-30f4a62e2ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8f147150-bf6a-41f0-b933-31cc4734a367" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8f147150-bf6a-41f0-b933-31cc4734a367" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_6e0f88fa-a602-4bb2-b118-f2a33c95388c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_6e0f88fa-a602-4bb2-b118-f2a33c95388c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_27aa00e4-0c44-416f-8fc3-5d05eb0368ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_72e2fcf9-3704-433c-9cc4-0e63d33e6d21" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_27aa00e4-0c44-416f-8fc3-5d05eb0368ee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_dd783d33-f5d0-4f6e-823d-cd9cc6b037d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6388194b-08a0-4c44-91c8-31f841e30caf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_aa4f3b4c-56e2-4793-8152-f45921a0f669" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_aa4f3b4c-56e2-4793-8152-f45921a0f669" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_432a308b-1918-4e4d-b110-d53b5f536c90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_432a308b-1918-4e4d-b110-d53b5f536c90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_df0928dd-c4c0-40b6-a38d-d5b67b456d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_df0928dd-c4c0-40b6-a38d-d5b67b456d0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d4f6a128-9506-4586-972a-a91e5ebf83b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_aa0fc67d-271b-4fbb-87e8-31c43153a0e0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d4f6a128-9506-4586-972a-a91e5ebf83b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_704c160c-9898-4b26-b6b6-38166b136e02" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/INCOMETAXESNarrativeDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#INCOMETAXESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/INCOMETAXESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_b98d00a8-8014-4f48-b5e9-b99b3bb4c515" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_b98d00a8-8014-4f48-b5e9-b99b3bb4c515" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_f857f3d9-225d-481c-9d0c-b0a34cd69373" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_b98d00a8-8014-4f48-b5e9-b99b3bb4c515" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_f857f3d9-225d-481c-9d0c-b0a34cd69373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_f857f3d9-225d-481c-9d0c-b0a34cd69373_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_f857f3d9-225d-481c-9d0c-b0a34cd69373" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_f857f3d9-225d-481c-9d0c-b0a34cd69373_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_1a4db028-77ea-49ea-9a54-99eb1243e39f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_f857f3d9-225d-481c-9d0c-b0a34cd69373" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_1a4db028-77ea-49ea-9a54-99eb1243e39f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_9f8a2204-6651-40f8-b230-571e7463c05f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_1a4db028-77ea-49ea-9a54-99eb1243e39f" xlink:to="loc_us-gaap_DomesticCountryMember_9f8a2204-6651-40f8-b230-571e7463c05f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_2a685a44-1339-41ac-a0a6-a4cd907b9fce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_1a4db028-77ea-49ea-9a54-99eb1243e39f" xlink:to="loc_us-gaap_ForeignCountryMember_2a685a44-1339-41ac-a0a6-a4cd907b9fce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_f8d97c72-39dd-470c-9a22-67aee8ab5907" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_1a4db028-77ea-49ea-9a54-99eb1243e39f" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_f8d97c72-39dd-470c-9a22-67aee8ab5907" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsValuationAllowance_c2775229-464c-455d-a02c-ac58a77e0040" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_OperatingLossCarryforwardsValuationAllowance_c2775229-464c-455d-a02c-ac58a77e0040" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_0f98cc6d-a578-46e9-b722-0cc1eb6e18bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_0f98cc6d-a578-46e9-b722-0cc1eb6e18bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationGiltiAmount_a8805111-7caf-4185-bbc5-7730cfdbefe2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationGiltiAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationGiltiAmount_a8805111-7caf-4185-bbc5-7730cfdbefe2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_32299f82-0146-49f3-bb12-70515a9fb79d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_OperatingLossCarryforwards_32299f82-0146-49f3-bb12-70515a9fb79d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_OperatingLossCarryforwardsSubjectToExpiration_90256ef6-f544-42d3-b0ba-be3db36960e2" xlink:href="notv-20240930.xsd#notv_OperatingLossCarryforwardsSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_notv_OperatingLossCarryforwardsSubjectToExpiration_90256ef6-f544-42d3-b0ba-be3db36960e2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_b8a912c5-f47d-4b24-b28e-efe1f1086f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_b8a912c5-f47d-4b24-b28e-efe1f1086f5e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_79c68771-72b2-4f99-a398-5d3a3fae9718" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_79c68771-72b2-4f99-a398-5d3a3fae9718" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_AcquiredForeignNetOperatingLosses_cbec6d97-cf87-43d1-be97-afaf269292ea" xlink:href="notv-20240930.xsd#notv_AcquiredForeignNetOperatingLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_2718c233-115a-470a-a824-af1ce625a6d8" xlink:to="loc_notv_AcquiredForeignNetOperatingLosses_cbec6d97-cf87-43d1-be97-afaf269292ea" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.inotivco.com/role/CONTINGENCIESDetails" xlink:type="simple" xlink:href="notv-20240930.xsd#CONTINGENCIESDetails"/>
  <link:definitionLink xlink:role="http://www.inotivco.com/role/CONTINGENCIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_24aee854-192e-42ce-b67d-dcaf508267e6" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_srt_StatementGeographicalAxis_24aee854-192e-42ce-b67d-dcaf508267e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_24aee854-192e-42ce-b67d-dcaf508267e6_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_24aee854-192e-42ce-b67d-dcaf508267e6" xlink:to="loc_srt_SegmentGeographicalDomain_24aee854-192e-42ce-b67d-dcaf508267e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_bdc5f2f1-4c88-405b-b74d-8f9ceb39b246" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_24aee854-192e-42ce-b67d-dcaf508267e6" xlink:to="loc_srt_SegmentGeographicalDomain_bdc5f2f1-4c88-405b-b74d-8f9ceb39b246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_KH_03c86e70-7b79-428d-8fd4-f5902160d7a6" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_KH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_bdc5f2f1-4c88-405b-b74d-8f9ceb39b246" xlink:to="loc_country_KH_03c86e70-7b79-428d-8fd4-f5902160d7a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b5e7ac3b-091a-4a97-b560-f1fb73d1e995" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b5e7ac3b-091a-4a97-b560-f1fb73d1e995" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_b5e7ac3b-091a-4a97-b560-f1fb73d1e995_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b5e7ac3b-091a-4a97-b560-f1fb73d1e995" xlink:to="loc_us-gaap_LossContingencyNatureDomain_b5e7ac3b-091a-4a97-b560-f1fb73d1e995_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b5e7ac3b-091a-4a97-b560-f1fb73d1e995" xlink:to="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResolutionAgreementAndPleaAgreementMember_dba9c1ec-6566-41ca-8e4b-c88ba79d4aec" xlink:href="notv-20240930.xsd#notv_ResolutionAgreementAndPleaAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:to="loc_notv_ResolutionAgreementAndPleaAgreementMember_dba9c1ec-6566-41ca-8e4b-c88ba79d4aec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_USDOJAgreementInPrincipleFinesMember_2c28d54e-1d32-470d-89b1-41370f479f29" xlink:href="notv-20240930.xsd#notv_USDOJAgreementInPrincipleFinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:to="loc_notv_USDOJAgreementInPrincipleFinesMember_2c28d54e-1d32-470d-89b1-41370f479f29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_USDOJAgreementInPrincipleMember_600e269b-4e08-4149-af4e-523b433ae99c" xlink:href="notv-20240930.xsd#notv_USDOJAgreementInPrincipleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:to="loc_notv_USDOJAgreementInPrincipleMember_600e269b-4e08-4149-af4e-523b433ae99c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_USDOJAgreementInPrincipleFacilityImprovementsMember_3cd73406-8920-461b-a4ba-8423a80142d8" xlink:href="notv-20240930.xsd#notv_USDOJAgreementInPrincipleFacilityImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_031d2cf1-b305-4187-8dc4-490cf2bae1a0" xlink:to="loc_notv_USDOJAgreementInPrincipleFacilityImprovementsMember_3cd73406-8920-461b-a4ba-8423a80142d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentTimingAxis_b82e0f25-435e-4ced-a86f-24d372d95690" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentTimingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_notv_LossContingencyPaymentTimingAxis_b82e0f25-435e-4ced-a86f-24d372d95690" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentTimingDomain_b82e0f25-435e-4ced-a86f-24d372d95690_default" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentTimingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_notv_LossContingencyPaymentTimingAxis_b82e0f25-435e-4ced-a86f-24d372d95690" xlink:to="loc_notv_LossContingencyPaymentTimingDomain_b82e0f25-435e-4ced-a86f-24d372d95690_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentTimingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_notv_LossContingencyPaymentTimingAxis_b82e0f25-435e-4ced-a86f-24d372d95690" xlink:to="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentPeriodOneMember_cd6bc934-5c90-4d65-a24d-bbb6a8e4cab8" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:to="loc_notv_LossContingencyPaymentPeriodOneMember_cd6bc934-5c90-4d65-a24d-bbb6a8e4cab8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentPeriodTwoMember_f0cc83b3-5e5c-43cb-894f-1f2f04620bf5" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:to="loc_notv_LossContingencyPaymentPeriodTwoMember_f0cc83b3-5e5c-43cb-894f-1f2f04620bf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentPeriodThreeMember_cadcab4e-42dc-4530-8798-0b184cee7022" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:to="loc_notv_LossContingencyPaymentPeriodThreeMember_cadcab4e-42dc-4530-8798-0b184cee7022" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyPaymentPeriodFourMember_eb75c54d-9de4-4e00-8b3e-f214f70be386" xlink:href="notv-20240930.xsd#notv_LossContingencyPaymentPeriodFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_notv_LossContingencyPaymentTimingDomain_16d4e7c4-4d88-45f2-b605-27e5e5f19f4d" xlink:to="loc_notv_LossContingencyPaymentPeriodFourMember_eb75c54d-9de4-4e00-8b3e-f214f70be386" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_039fa429-87ee-44a2-bfb5-548289e625f5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_srt_CounterpartyNameAxis_039fa429-87ee-44a2-bfb5-548289e625f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_039fa429-87ee-44a2-bfb5-548289e625f5_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_039fa429-87ee-44a2-bfb5-548289e625f5" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_039fa429-87ee-44a2-bfb5-548289e625f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4383aa8c-5198-4669-96d5-28fa4f6d1f9e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_039fa429-87ee-44a2-bfb5-548289e625f5" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4383aa8c-5198-4669-96d5-28fa4f6d1f9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_VirginiaAnimalFightingTaskforceAndHumaneSocietyUnitedStatesMember_1fd62e27-5c7c-4332-8d1f-d0eb246fda4e" xlink:href="notv-20240930.xsd#notv_VirginiaAnimalFightingTaskforceAndHumaneSocietyUnitedStatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4383aa8c-5198-4669-96d5-28fa4f6d1f9e" xlink:to="loc_notv_VirginiaAnimalFightingTaskforceAndHumaneSocietyUnitedStatesMember_1fd62e27-5c7c-4332-8d1f-d0eb246fda4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_NationalFishAndWildlifeFoundationMember_027a6fc0-0bb5-48fb-9d71-59909a034537" xlink:href="notv-20240930.xsd#notv_NationalFishAndWildlifeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4383aa8c-5198-4669-96d5-28fa4f6d1f9e" xlink:to="loc_notv_NationalFishAndWildlifeFoundationMember_027a6fc0-0bb5-48fb-9d71-59909a034537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_a8fdce2c-a4dd-443b-8c29-579bd1a8e475" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_a8fdce2c-a4dd-443b-8c29-579bd1a8e475" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_a8fdce2c-a4dd-443b-8c29-579bd1a8e475_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a8fdce2c-a4dd-443b-8c29-579bd1a8e475" xlink:to="loc_us-gaap_SegmentDomain_a8fdce2c-a4dd-443b-8c29-579bd1a8e475_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_47c9a630-a98c-4648-8a3e-aca3e36f6c81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a8fdce2c-a4dd-443b-8c29-579bd1a8e475" xlink:to="loc_us-gaap_SegmentDomain_47c9a630-a98c-4648-8a3e-aca3e36f6c81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_ResearchModelsAndServicesSegmentMember_55460830-31f8-494d-906e-6e3be17b2d7a" xlink:href="notv-20240930.xsd#notv_ResearchModelsAndServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_47c9a630-a98c-4648-8a3e-aca3e36f6c81" xlink:to="loc_notv_ResearchModelsAndServicesSegmentMember_55460830-31f8-494d-906e-6e3be17b2d7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_005226b3-63f4-461e-a747-3a6ae60e4a81" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_86e1e85a-38fc-47af-a762-cc70c4f28dcb" xlink:to="loc_srt_RangeAxis_005226b3-63f4-461e-a747-3a6ae60e4a81" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_005226b3-63f4-461e-a747-3a6ae60e4a81_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_005226b3-63f4-461e-a747-3a6ae60e4a81" xlink:to="loc_srt_RangeMember_005226b3-63f4-461e-a747-3a6ae60e4a81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fe0bc415-d8e9-46f6-93a8-2b6b84dc6fb5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_005226b3-63f4-461e-a747-3a6ae60e4a81" xlink:to="loc_srt_RangeMember_fe0bc415-d8e9-46f6-93a8-2b6b84dc6fb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_e0b291ce-b421-47dc-91ea-6fbcac783aca" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fe0bc415-d8e9-46f6-93a8-2b6b84dc6fb5" xlink:to="loc_srt_MinimumMember_e0b291ce-b421-47dc-91ea-6fbcac783aca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c77c497a-fb55-4358-99e3-b656f8057253" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fe0bc415-d8e9-46f6-93a8-2b6b84dc6fb5" xlink:to="loc_srt_MaximumMember_c77c497a-fb55-4358-99e3-b656f8057253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_3f7b83ce-01bf-411b-9ff3-bb487e767bed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_3f7b83ce-01bf-411b-9ff3-bb487e767bed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_0e1d22cf-fe4f-42a4-915c-b623d2b30648" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfGovernmentOfficialsIncluded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyNumberOfGovernmentOfficialsIncluded_0e1d22cf-fe4f-42a4-915c-b623d2b30648" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyNumberOfImports_58434164-9941-4f2f-97c3-326e564547c3" xlink:href="notv-20240930.xsd#notv_LossContingencyNumberOfImports"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyNumberOfImports_58434164-9941-4f2f-97c3-326e564547c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_9f58e392-a98a-47d9-85ca-4eb3795e5e6e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_9f58e392-a98a-47d9-85ca-4eb3795e5e6e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyLiensCapacityOfAdditionalDebtToBeSecured_d69ad4da-65a2-4913-a8fe-d49b217bf5e1" xlink:href="notv-20240930.xsd#notv_LossContingencyLiensCapacityOfAdditionalDebtToBeSecured"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyLiensCapacityOfAdditionalDebtToBeSecured_d69ad4da-65a2-4913-a8fe-d49b217bf5e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualProvision_5b725f17-4475-40d1-975d-086d2fb9d015" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyAccrualProvision"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingencyAccrualProvision_5b725f17-4475-40d1-975d-086d2fb9d015" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualPayments_7c42c71a-f8ec-4bc3-bfab-2c99a41d2549" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyAccrualPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingencyAccrualPayments_7c42c71a-f8ec-4bc3-bfab-2c99a41d2549" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualCarryingValueCurrent_21effdbc-ef50-4ab4-9068-b90cc36eaef6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyAccrualCarryingValueCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingencyAccrualCarryingValueCurrent_21effdbc-ef50-4ab4-9068-b90cc36eaef6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualCarryingValueNoncurrent_552c51f1-0665-45e4-a6dc-e72f19619db1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LossContingencyAccrualCarryingValueNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_us-gaap_LossContingencyAccrualCarryingValueNoncurrent_552c51f1-0665-45e4-a6dc-e72f19619db1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyEstimatedLossPeriod_3a7df0df-c08f-4f2f-87b5-cb0cba7ab205" xlink:href="notv-20240930.xsd#notv_LossContingencyEstimatedLossPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyEstimatedLossPeriod_3a7df0df-c08f-4f2f-87b5-cb0cba7ab205" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfSelectionProcess_68c4ce77-23c2-4300-829b-87160eadea28" xlink:href="notv-20240930.xsd#notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfSelectionProcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfSelectionProcess_68c4ce77-23c2-4300-829b-87160eadea28" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfProbation_f1f7e278-a833-443d-9bca-d8d34d4dd7fb" xlink:href="notv-20240930.xsd#notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfProbation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyMonitorshipExpirationPeriodPeriodAfterCompletionOfProbation_f1f7e278-a833-443d-9bca-d8d34d4dd7fb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_notv_LossContingencyProbationPeriod_7d8ac638-50ea-415e-a336-e878a6033b94" xlink:href="notv-20240930.xsd#notv_LossContingencyProbationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_10b58bb9-704f-4ca6-8676-df4c2049b4fc" xlink:to="loc_notv_LossContingencyProbationPeriod_7d8ac638-50ea-415e-a336-e878a6033b94" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#AwardTypeOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockMember" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_us-gaap_InterestExpenseNonoperating" xlink:type="arc" order="691"/>
  </link:definitionLink>
</link:linkbase>
