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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:fe4f5c01-200f-48ed-bf24-67c72c619942,g:31d16e15-9abe-4b62-be1f-44cfd88a9788-->
<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.alx-inc.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="simple" xlink:href="alx-20210930.xsd#ConsolidatedStatementsofChangesinEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="extended" id="if379b538ca364a5cab682ba25b3545c7_ConsolidatedStatementsofChangesinEquityUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_f4c1dec1-ae20-483a-b29b-9ea470b79af3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_f4c1dec1-ae20-483a-b29b-9ea470b79af3" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_c9c68617-9947-41d4-ab96-4e31e29122e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_CommonStockSharesIssued_c9c68617-9947-41d4-ab96-4e31e29122e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_c01a04c1-27e4-4f95-a4d5-9fe0674af3a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_StockholdersEquity_c01a04c1-27e4-4f95-a4d5-9fe0674af3a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_b7d9bfaa-51f7-4cf2-8aae-bc777bd94bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_NetIncomeLoss_b7d9bfaa-51f7-4cf2-8aae-bc777bd94bfe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_eeff9589-d9fe-4327-b999-5dc6f0d32414" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_DividendsCommonStockCash_eeff9589-d9fe-4327-b999-5dc6f0d32414" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_1de72896-099e-4002-a2e9-ac2b5cc589b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_1de72896-099e-4002-a2e9-ac2b5cc589b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_be8afed4-3fbf-4091-afd7-823dac951d37" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d55f9955-7ecf-41a1-98c7-6955dc0bf009" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_be8afed4-3fbf-4091-afd7-823dac951d37" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_1fcfb3b0-f717-43c8-b366-028eebd5ee41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_6e170c99-1822-4fb6-9215-8e72493ad2bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_967e2f93-50a3-4e9c-a0d9-637fe7384cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_f4c1dec1-ae20-483a-b29b-9ea470b79af3" xlink:to="loc_us-gaap_StatementTable_967e2f93-50a3-4e9c-a0d9-637fe7384cbe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8aebf5cc-b3db-462c-b16b-94297e7c761f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_967e2f93-50a3-4e9c-a0d9-637fe7384cbe" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8aebf5cc-b3db-462c-b16b-94297e7c761f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8aebf5cc-b3db-462c-b16b-94297e7c761f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8aebf5cc-b3db-462c-b16b-94297e7c761f" xlink:to="loc_us-gaap_EquityComponentDomain_8aebf5cc-b3db-462c-b16b-94297e7c761f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8aebf5cc-b3db-462c-b16b-94297e7c761f" xlink:to="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_98c5bb51-e961-4755-af95-b7da9ee181fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:to="loc_us-gaap_CommonStockMember_98c5bb51-e961-4755-af95-b7da9ee181fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_348851fc-3b76-44cd-abba-76b112783a72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_348851fc-3b76-44cd-abba-76b112783a72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_594d5320-7ea8-4f93-8cbd-89d2bbdf2b46" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:to="loc_us-gaap_RetainedEarningsMember_594d5320-7ea8-4f93-8cbd-89d2bbdf2b46" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_da20232e-fd32-465f-8bf1-b8d15f9847e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_da20232e-fd32-465f-8bf1-b8d15f9847e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_473a26e5-8df6-4289-ab51-fc46c9731426" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f08a0b1c-5958-4e08-a0be-acb32760cd35" xlink:to="loc_us-gaap_TreasuryStockMember_473a26e5-8df6-4289-ab51-fc46c9731426" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsofCashFlowsUnauditedParenthetical" xlink:type="simple" xlink:href="alx-20210930.xsd#ConsolidatedStatementsofCashFlowsUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsofCashFlowsUnauditedParenthetical" xlink:type="extended" id="if6a587769bf94642b6c1be1cc2253295_ConsolidatedStatementsofCashFlowsUnauditedParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0ed80302-896c-41f3-853a-7eeefc42342e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NonCashAdditionsToRealEstate_18ede1af-1dc1-46a7-bb68-255cf3ddecc1" xlink:href="alx-20210930.xsd#alx_NonCashAdditionsToRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0ed80302-896c-41f3-853a-7eeefc42342e" xlink:to="loc_alx_NonCashAdditionsToRealEstate_18ede1af-1dc1-46a7-bb68-255cf3ddecc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_0b4ce739-f9fd-4851-9843-b3b87217101c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0ed80302-896c-41f3-853a-7eeefc42342e" xlink:to="loc_us-gaap_StatementTable_0b4ce739-f9fd-4851-9843-b3b87217101c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_ff40e76d-76ef-4389-8d6e-bd7600254fc0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0b4ce739-f9fd-4851-9843-b3b87217101c" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_ff40e76d-76ef-4389-8d6e-bd7600254fc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_ff40e76d-76ef-4389-8d6e-bd7600254fc0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_ff40e76d-76ef-4389-8d6e-bd7600254fc0" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_ff40e76d-76ef-4389-8d6e-bd7600254fc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_efd3a12a-23a1-4f7d-baff-a4b40c18e3cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_ff40e76d-76ef-4389-8d6e-bd7600254fc0" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_efd3a12a-23a1-4f7d-baff-a4b40c18e3cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeesMember_1cf499b1-2544-4b20-9b5e-54831adce3b3" xlink:href="alx-20210930.xsd#alx_DevelopmentFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_efd3a12a-23a1-4f7d-baff-a4b40c18e3cc" xlink:to="loc_alx_DevelopmentFeesMember_1cf499b1-2544-4b20-9b5e-54831adce3b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_26945250-9f97-43da-95e0-bdaf8fe42b44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0b4ce739-f9fd-4851-9843-b3b87217101c" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_26945250-9f97-43da-95e0-bdaf8fe42b44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_26945250-9f97-43da-95e0-bdaf8fe42b44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_26945250-9f97-43da-95e0-bdaf8fe42b44" xlink:to="loc_us-gaap_RelatedPartyDomain_26945250-9f97-43da-95e0-bdaf8fe42b44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_23381fca-9879-4562-bcab-ad2a3a368cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_26945250-9f97-43da-95e0-bdaf8fe42b44" xlink:to="loc_us-gaap_RelatedPartyDomain_23381fca-9879-4562-bcab-ad2a3a368cbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_f61567f3-1d35-4756-83e8-cb2995ef7baf" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_23381fca-9879-4562-bcab-ad2a3a368cbd" xlink:to="loc_srt_AffiliatedEntityMember_f61567f3-1d35-4756-83e8-cb2995ef7baf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="alx-20210930.xsd#RevenueRecognitionDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionDisaggregationofRevenueDetails" xlink:type="extended" id="i530e9ebdbd4a427fa0c8df7d5173ccf1_RevenueRecognitionDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_53f3f2fe-9f6e-4b0c-a030-5d41af9210ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_bfef9915-892c-4f6a-921e-442aa38c3e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_53f3f2fe-9f6e-4b0c-a030-5d41af9210ee" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_bfef9915-892c-4f6a-921e-442aa38c3e5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3795b3c1-aea4-4448-8a18-fa995b88e8a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_53f3f2fe-9f6e-4b0c-a030-5d41af9210ee" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3795b3c1-aea4-4448-8a18-fa995b88e8a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_331f4ab7-6b57-491d-acfa-61647c7f09e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_53f3f2fe-9f6e-4b0c-a030-5d41af9210ee" xlink:to="loc_us-gaap_Revenues_331f4ab7-6b57-491d-acfa-61647c7f09e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_af6639fc-bf45-4766-8451-c35f5fd86e4d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_53f3f2fe-9f6e-4b0c-a030-5d41af9210ee" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_af6639fc-bf45-4766-8451-c35f5fd86e4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_43c729ec-1928-4985-98fa-697ae834aa58" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_af6639fc-bf45-4766-8451-c35f5fd86e4d" xlink:to="loc_srt_ProductOrServiceAxis_43c729ec-1928-4985-98fa-697ae834aa58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_43c729ec-1928-4985-98fa-697ae834aa58_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_43c729ec-1928-4985-98fa-697ae834aa58" xlink:to="loc_srt_ProductsAndServicesDomain_43c729ec-1928-4985-98fa-697ae834aa58_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_bf2471be-0967-42c2-9010-0717ddf3aeac" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_43c729ec-1928-4985-98fa-697ae834aa58" xlink:to="loc_srt_ProductsAndServicesDomain_bf2471be-0967-42c2-9010-0717ddf3aeac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParkingMember_3895fcfe-8cc1-469d-b0aa-4c915cd25273" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ParkingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bf2471be-0967-42c2-9010-0717ddf3aeac" xlink:to="loc_us-gaap_ParkingMember_3895fcfe-8cc1-469d-b0aa-4c915cd25273" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DirectServicesMember_04a2e98c-92a1-414f-8769-02df4ba9d8de" xlink:href="alx-20210930.xsd#alx_DirectServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bf2471be-0967-42c2-9010-0717ddf3aeac" xlink:to="loc_alx_DirectServicesMember_04a2e98c-92a1-414f-8769-02df4ba9d8de" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:type="simple" xlink:href="alx-20210930.xsd#RevenueRecognitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:type="extended" id="ic2dbc1d637cf47fea2a30a163267a612_RevenueRecognitionNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_850928ef-1786-46ce-af3c-ca4d36584070" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_62422013-7a29-46d7-b80d-63b1ad6fd681" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_850928ef-1786-46ce-af3c-ca4d36584070" xlink:to="loc_us-gaap_Revenues_62422013-7a29-46d7-b80d-63b1ad6fd681" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_54df1cfc-544b-4183-8dd5-45a04bf6f1b7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_850928ef-1786-46ce-af3c-ca4d36584070" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_54df1cfc-544b-4183-8dd5-45a04bf6f1b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_aef736d5-4826-4a83-a347-8a1aa82a64b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_850928ef-1786-46ce-af3c-ca4d36584070" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_aef736d5-4826-4a83-a347-8a1aa82a64b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aef736d5-4826-4a83-a347-8a1aa82a64b6" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_863498ef-4080-49c7-9d1f-f610f7878022" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_c4e79f67-5bf9-4ea1-9d4c-85d8a52c1736" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_863498ef-4080-49c7-9d1f-f610f7878022" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_8a2669c9-a2eb-42c6-b1c9-1b05398d4205" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_863498ef-4080-49c7-9d1f-f610f7878022" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_8a2669c9-a2eb-42c6-b1c9-1b05398d4205" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_65a2e088-e99f-4496-a9b8-78bdb7e16827" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aef736d5-4826-4a83-a347-8a1aa82a64b6" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_65a2e088-e99f-4496-a9b8-78bdb7e16827" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_65a2e088-e99f-4496-a9b8-78bdb7e16827_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_65a2e088-e99f-4496-a9b8-78bdb7e16827" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_65a2e088-e99f-4496-a9b8-78bdb7e16827_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0abb7e09-052b-42f6-bcf4-173c83702eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_65a2e088-e99f-4496-a9b8-78bdb7e16827" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0abb7e09-052b-42f6-bcf4-173c83702eb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_2139590c-9ecb-4b59-a69c-9115c39f8667" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_0abb7e09-052b-42f6-bcf4-173c83702eb8" xlink:to="loc_us-gaap_SalesRevenueNetMember_2139590c-9ecb-4b59-a69c-9115c39f8667" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_63280659-7cec-4161-9931-e2c723422d75" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aef736d5-4826-4a83-a347-8a1aa82a64b6" xlink:to="loc_srt_MajorCustomersAxis_63280659-7cec-4161-9931-e2c723422d75" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_63280659-7cec-4161-9931-e2c723422d75_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_63280659-7cec-4161-9931-e2c723422d75" xlink:to="loc_srt_NameOfMajorCustomerDomain_63280659-7cec-4161-9931-e2c723422d75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_df2093fe-eb77-4cdd-b5c0-8561c8976929" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_63280659-7cec-4161-9931-e2c723422d75" xlink:to="loc_srt_NameOfMajorCustomerDomain_df2093fe-eb77-4cdd-b5c0-8561c8976929" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_BloombergMember_39f1d244-bcda-4fbd-8209-dfa0adc33861" xlink:href="alx-20210930.xsd#alx_BloombergMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_df2093fe-eb77-4cdd-b5c0-8561c8976929" xlink:to="loc_alx_BloombergMember_39f1d244-bcda-4fbd-8209-dfa0adc33861" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RealEstateSalesNarrativeDetails" xlink:type="simple" xlink:href="alx-20210930.xsd#RealEstateSalesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RealEstateSalesNarrativeDetails" xlink:type="extended" id="i2c6f62158bd448a390001b918ea2040f_RealEstateSalesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ProceedsFromSaleOfLandHeldForInvestmentExcludingDisposalCost_d7764016-657f-4c6b-bf77-92794ce175ff" xlink:href="alx-20210930.xsd#alx_ProceedsFromSaleOfLandHeldForInvestmentExcludingDisposalCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:to="loc_alx_ProceedsFromSaleOfLandHeldForInvestmentExcludingDisposalCost_d7764016-657f-4c6b-bf77-92794ce175ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfLandHeldforinvestment_540e6f66-de9b-44f7-b16e-cef265eff102" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfLandHeldforinvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:to="loc_us-gaap_ProceedsFromSaleOfLandHeldforinvestment_540e6f66-de9b-44f7-b16e-cef265eff102" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnSalesOfInvestmentRealEstate_fd99bbd2-d548-4693-a39e-6d93a1b465d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainsLossesOnSalesOfInvestmentRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:to="loc_us-gaap_GainsLossesOnSalesOfInvestmentRealEstate_fd99bbd2-d548-4693-a39e-6d93a1b465d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ProceedsFromSaleOfLandHeldForInvestmentNet_d61462c5-87ee-466b-99a0-638367f14d5a" xlink:href="alx-20210930.xsd#alx_ProceedsFromSaleOfLandHeldForInvestmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:to="loc_alx_ProceedsFromSaleOfLandHeldForInvestmentNet_d61462c5-87ee-466b-99a0-638367f14d5a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RealEstateTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RealEstateLineItems_53c914c2-d9f7-49bb-9115-265ef2563673" xlink:to="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantAxis_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:to="loc_alx_RealEstatePropertyOccupantAxis_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4_default" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_f8edc37b-e290-47c8-8630-2fac462eadc9" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_44b9bd70-f4c9-4a7b-8643-a2f3c7f8a3c4" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_f8edc37b-e290-47c8-8630-2fac462eadc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_IkeaMember_49405758-848c-4155-89a6-976859b38a29" xlink:href="alx-20210930.xsd#alx_IkeaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_f8edc37b-e290-47c8-8630-2fac462eadc9" xlink:to="loc_alx_IkeaMember_49405758-848c-4155-89a6-976859b38a29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_d7f18826-8b0f-4678-96ea-13ca9b642a44" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_ef4db3c2-4c0a-48e9-a0f6-adfbb753e5a9" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_d7f18826-8b0f-4678-96ea-13ca9b642a44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TenantOccupantMember_cf9d5be3-fe76-4fce-ad87-95dfeab66b88" xlink:href="alx-20210930.xsd#alx_TenantOccupantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_d7f18826-8b0f-4678-96ea-13ca9b642a44" xlink:to="loc_alx_TenantOccupantMember_cf9d5be3-fe76-4fce-ad87-95dfeab66b88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_817740db-7f33-4181-b24a-4e85b7b4046d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_817740db-7f33-4181-b24a-4e85b7b4046d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_817740db-7f33-4181-b24a-4e85b7b4046d_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_817740db-7f33-4181-b24a-4e85b7b4046d" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_817740db-7f33-4181-b24a-4e85b7b4046d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_cb6896f5-d5dd-4c35-bf8f-103977061b36" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_817740db-7f33-4181-b24a-4e85b7b4046d" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_cb6896f5-d5dd-4c35-bf8f-103977061b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_BronxLandParcelMember_bc891547-7a21-40ef-837f-8e299f6a5452" xlink:href="alx-20210930.xsd#alx_BronxLandParcelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_cb6896f5-d5dd-4c35-bf8f-103977061b36" xlink:to="loc_alx_BronxLandParcelMember_bc891547-7a21-40ef-837f-8e299f6a5452" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ParamusPropertyMember_b3e50310-db7c-4bf1-8cff-33298e6d043a" xlink:href="alx-20210930.xsd#alx_ParamusPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_cb6896f5-d5dd-4c35-bf8f-103977061b36" xlink:to="loc_alx_ParamusPropertyMember_b3e50310-db7c-4bf1-8cff-33298e6d043a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_a27ef88e-446e-4618-bcab-171508cc96f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_a27ef88e-446e-4618-bcab-171508cc96f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_a27ef88e-446e-4618-bcab-171508cc96f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_a27ef88e-446e-4618-bcab-171508cc96f2" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_a27ef88e-446e-4618-bcab-171508cc96f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_940a58b3-fb05-4941-9ae8-54db092461d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_a27ef88e-446e-4618-bcab-171508cc96f2" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_940a58b3-fb05-4941-9ae8-54db092461d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_a747d5d4-89db-4825-b441-ef22c0d47338" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_940a58b3-fb05-4941-9ae8-54db092461d6" xlink:to="loc_us-gaap_SubsequentEventMember_a747d5d4-89db-4825-b441-ef22c0d47338" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_b14b9211-3ee9-4c33-afbb-ee2826d46672" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RealEstateTable_e9265752-9ced-48f7-a414-dc87a88bfd27" xlink:to="loc_srt_StatementScenarioAxis_b14b9211-3ee9-4c33-afbb-ee2826d46672" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_b14b9211-3ee9-4c33-afbb-ee2826d46672_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_b14b9211-3ee9-4c33-afbb-ee2826d46672" xlink:to="loc_srt_ScenarioUnspecifiedDomain_b14b9211-3ee9-4c33-afbb-ee2826d46672_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_ace999cb-dd4e-4fea-adf0-5e598e18ac60" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_b14b9211-3ee9-4c33-afbb-ee2826d46672" xlink:to="loc_srt_ScenarioUnspecifiedDomain_ace999cb-dd4e-4fea-adf0-5e598e18ac60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_c73a87d8-5abe-41c3-b3f0-a1227a22dbf5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_ace999cb-dd4e-4fea-adf0-5e598e18ac60" xlink:to="loc_srt_ScenarioForecastMember_c73a87d8-5abe-41c3-b3f0-a1227a22dbf5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsAdditionalInformationDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#RelatedPartyTransactionsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsAdditionalInformationDetail" xlink:type="extended" id="i3cd9bc10e6534543bbe2e013c2f7895a_RelatedPartyTransactionsAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_b34cff06-f45e-4437-9c6d-0816dedee8b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_b34cff06-f45e-4437-9c6d-0816dedee8b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ManagementFeeAgreementValue_15f3cdff-36f1-4044-88dd-84bbddd05124" xlink:href="alx-20210930.xsd#alx_ManagementFeeAgreementValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_ManagementFeeAgreementValue_15f3cdff-36f1-4044-88dd-84bbddd05124" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyManagementFeePercentFee_0f4df240-77d6-401b-9f94-aad751157887" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyManagementFeePercentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_us-gaap_PropertyManagementFeePercentFee_0f4df240-77d6-401b-9f94-aad751157887" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_c707fb7b-1b3b-4907-a08e-64693bd6d112" xlink:href="alx-20210930.xsd#alx_PropertyManagementFeeAgreementPricePerSquareFoot"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_c707fb7b-1b3b-4907-a08e-64693bd6d112" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeeAgreementValue_9e35abde-1350-458f-a050-5e7a1d7803bb" xlink:href="alx-20210930.xsd#alx_PropertyManagementFeeAgreementValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PropertyManagementFeeAgreementValue_9e35abde-1350-458f-a050-5e7a1d7803bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_cfa989d4-9a25-4702-b698-390c608e8e3d" xlink:href="alx-20210930.xsd#alx_PropertyManagementFeeEscalationPercentagePerAnnum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_cfa989d4-9a25-4702-b698-390c608e8e3d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeePercentage_2cc5af9a-9ccf-419f-b8f4-73dccc1240b9" xlink:href="alx-20210930.xsd#alx_DevelopmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_DevelopmentFeePercentage_2cc5af9a-9ccf-419f-b8f4-73dccc1240b9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentOneToTenYears_34455611-5755-4c09-9b27-4e0b4d312203" xlink:href="alx-20210930.xsd#alx_LeaseFeePercentageOfRentOneToTenYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_LeaseFeePercentageOfRentOneToTenYears_34455611-5755-4c09-9b27-4e0b4d312203" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_f0ec8584-07fe-4f9c-bcf5-18262ef1b363" xlink:href="alx-20210930.xsd#alx_LeaseFeePercentageOfRentElevenToTwentyYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_f0ec8584-07fe-4f9c-bcf5-18262ef1b363" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_eb93eaf2-7f80-4efb-a584-5cdf8b55c672" xlink:href="alx-20210930.xsd#alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_eb93eaf2-7f80-4efb-a584-5cdf8b55c672" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PercentageIncreaseLeaseFeeIfBrokerUsed_b18a5367-cf3b-430a-b340-75a5098a4a74" xlink:href="alx-20210930.xsd#alx_PercentageIncreaseLeaseFeeIfBrokerUsed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PercentageIncreaseLeaseFeeIfBrokerUsed_b18a5367-cf3b-430a-b340-75a5098a4a74" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_bb683c9a-58ad-4458-a6fd-983b96393569" xlink:href="alx-20210930.xsd#alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_bb683c9a-58ad-4458-a6fd-983b96393569" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AssetSaleCommissionThreshold_cb349631-c134-48ed-b137-03f79d4bb1bc" xlink:href="alx-20210930.xsd#alx_AssetSaleCommissionThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_AssetSaleCommissionThreshold_cb349631-c134-48ed-b137-03f79d4bb1bc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_11ec917c-60f5-44f2-a25d-88d2a20f062b" xlink:href="alx-20210930.xsd#alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_11ec917c-60f5-44f2-a25d-88d2a20f062b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForCommissions_466b22d6-e870-4fac-9bda-5bd2c6642145" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_us-gaap_PaymentsForCommissions_466b22d6-e870-4fac-9bda-5bd2c6642145" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedParty_dbb8eee1-e076-43e9-b8ed-e08d2ad85b71" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDueFromToRelatedParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedParty_dbb8eee1-e076-43e9-b8ed-e08d2ad85b71" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_3aabf56e-4e71-48e6-a56e-4d7edb915b89" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5491b7e1-a965-408e-bddf-60a52287b813" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_dei_LegalEntityAxis_5491b7e1-a965-408e-bddf-60a52287b813" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5491b7e1-a965-408e-bddf-60a52287b813_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5491b7e1-a965-408e-bddf-60a52287b813" xlink:to="loc_dei_EntityDomain_5491b7e1-a965-408e-bddf-60a52287b813_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_efc3d542-c697-40d5-8f5b-1a1cb830c600" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5491b7e1-a965-408e-bddf-60a52287b813" xlink:to="loc_dei_EntityDomain_efc3d542-c697-40d5-8f5b-1a1cb830c600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_VornadoMember_55659f88-9366-42f2-acf9-011e9adfb3a0" xlink:href="alx-20210930.xsd#alx_VornadoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_efc3d542-c697-40d5-8f5b-1a1cb830c600" xlink:to="loc_alx_VornadoMember_55659f88-9366-42f2-acf9-011e9adfb3a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_srt_OwnershipAxis_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc" xlink:to="loc_srt_OwnershipDomain_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_0a1c7fc5-f37a-477d-94f5-cf69c6b740e6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_e1aaf588-8ee8-4480-920b-7f2c72f8f6cc" xlink:to="loc_srt_OwnershipDomain_0a1c7fc5-f37a-477d-94f5-cf69c6b740e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AlexandersInc.Member_90999a5c-d9e3-408f-b95a-1e044c8df6a7" xlink:href="alx-20210930.xsd#alx_AlexandersInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_0a1c7fc5-f37a-477d-94f5-cf69c6b740e6" xlink:to="loc_alx_AlexandersInc.Member_90999a5c-d9e3-408f-b95a-1e044c8df6a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07" xlink:to="loc_us-gaap_RelatedPartyDomain_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_c046835a-0218-4edb-9518-4d4cdb65faa4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_0b945220-8e37-4fe9-a3d7-2eb8e3bf1e07" xlink:to="loc_us-gaap_RelatedPartyDomain_c046835a-0218-4edb-9518-4d4cdb65faa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_c78ba43d-f116-4aeb-8ed4-fb5e614f4979" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_c046835a-0218-4edb-9518-4d4cdb65faa4" xlink:to="loc_srt_AffiliatedEntityMember_c78ba43d-f116-4aeb-8ed4-fb5e614f4979" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_39d5dc1c-eb9b-4107-b8ca-8f8fd6abb040" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeesMember_6b797868-7e3c-4f9e-9bfa-2e0555104066" xlink:href="alx-20210930.xsd#alx_PropertyManagementFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:to="loc_alx_PropertyManagementFeesMember_6b797868-7e3c-4f9e-9bfa-2e0555104066" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeasingFeesMember_78b478ca-eb84-467d-8833-e80494435625" xlink:href="alx-20210930.xsd#alx_LeasingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:to="loc_alx_LeasingFeesMember_78b478ca-eb84-467d-8833-e80494435625" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeesMember_dc230f93-4ac7-44b8-ba94-9cc48abf4e81" xlink:href="alx-20210930.xsd#alx_DevelopmentFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:to="loc_alx_DevelopmentFeesMember_dc230f93-4ac7-44b8-ba94-9cc48abf4e81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember_df202131-9750-43d1-a4ef-55132b4664da" xlink:href="alx-20210930.xsd#alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_e2e3e427-f85d-4cb8-b91e-6e94f204b2a6" xlink:to="loc_alx_ManagementPropertyManagementCleaningEngineeringAndSecurityFeesMember_df202131-9750-43d1-a4ef-55132b4664da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_e7067df0-605b-409c-8e9d-b55cfb8d0fa5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_9d2d6640-5d08-4e35-9ab8-ea54ef94aeae" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_e7067df0-605b-409c-8e9d-b55cfb8d0fa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoPark2PropertyMember_bfffa0b5-7fc4-4f34-82e6-76e38d7b0632" xlink:href="alx-20210930.xsd#alx_RegoPark2PropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_e7067df0-605b-409c-8e9d-b55cfb8d0fa5" xlink:to="loc_alx_RegoPark2PropertyMember_bfffa0b5-7fc4-4f34-82e6-76e38d7b0632" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_a57a5dba-cff3-4c28-be0d-4b85dbf7a77f" xlink:href="alx-20210930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_e7067df0-605b-409c-8e9d-b55cfb8d0fa5" xlink:to="loc_alx_LexingtonAvenuePropertyMember_a57a5dba-cff3-4c28-be0d-4b85dbf7a77f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_b66be607-b787-4c67-8b2c-05565e81816d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_b66be607-b787-4c67-8b2c-05565e81816d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_b66be607-b787-4c67-8b2c-05565e81816d_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_b66be607-b787-4c67-8b2c-05565e81816d" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_b66be607-b787-4c67-8b2c-05565e81816d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_c631a739-4b71-4aad-8510-3be20637b661" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_b66be607-b787-4c67-8b2c-05565e81816d" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_c631a739-4b71-4aad-8510-3be20637b661" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_219dffa6-0549-4040-aabf-e014284dca5b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_c631a739-4b71-4aad-8510-3be20637b661" xlink:to="loc_srt_RetailSiteMember_219dffa6-0549-4040-aabf-e014284dca5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_OfficeAndRetailSpaceMember_7e1d2e52-0c2a-48fb-afc0-c89796251d2c" xlink:href="alx-20210930.xsd#alx_OfficeAndRetailSpaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_c631a739-4b71-4aad-8510-3be20637b661" xlink:to="loc_alx_OfficeAndRetailSpaceMember_7e1d2e52-0c2a-48fb-afc0-c89796251d2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CommonAreaMember_74aec42e-e7e4-4de4-9a3e-26d172d6d4d1" xlink:href="alx-20210930.xsd#alx_CommonAreaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_c631a739-4b71-4aad-8510-3be20637b661" xlink:to="loc_alx_CommonAreaMember_74aec42e-e7e4-4de4-9a3e-26d172d6d4d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_1def84de-4ed8-48ec-b8ab-18e39e2c8197" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_35e3d748-543e-4bf3-96d7-92cab45cfcb3" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_1def84de-4ed8-48ec-b8ab-18e39e2c8197" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_1def84de-4ed8-48ec-b8ab-18e39e2c8197_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1def84de-4ed8-48ec-b8ab-18e39e2c8197" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_1def84de-4ed8-48ec-b8ab-18e39e2c8197_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ca366834-3351-426a-923a-1d81e2fb6a73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1def84de-4ed8-48ec-b8ab-18e39e2c8197" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ca366834-3351-426a-923a-1d81e2fb6a73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_75f4302f-ce59-41de-af79-307fd3dd1f48" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_ca366834-3351-426a-923a-1d81e2fb6a73" xlink:to="loc_us-gaap_SubsequentEventMember_75f4302f-ce59-41de-af79-307fd3dd1f48" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsSummaryofFeestoVornadoDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#RelatedPartyTransactionsSummaryofFeestoVornadoDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsSummaryofFeestoVornadoDetail" xlink:type="extended" id="iac6e23e9d5054a40b2ad428c31f5f21f_RelatedPartyTransactionsSummaryofFeestoVornadoDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_5d0dd68b-3bd7-42d7-a66a-de8abffa33a0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty_df90e895-90c3-418f-9085-542c5adea5fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_5d0dd68b-3bd7-42d7-a66a-de8abffa33a0" xlink:to="loc_us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty_df90e895-90c3-418f-9085-542c5adea5fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_05b0f607-e71a-46f1-9c3a-736390452248" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_5d0dd68b-3bd7-42d7-a66a-de8abffa33a0" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_05b0f607-e71a-46f1-9c3a-736390452248" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_05b0f607-e71a-46f1-9c3a-736390452248" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_9d67d5fa-0275-4bcc-9743-2cc9b0f657ac" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CompanyManagementFeesMember_3ea43ba0-0969-4880-8ce0-467e4293f64a" xlink:href="alx-20210930.xsd#alx_CompanyManagementFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:to="loc_alx_CompanyManagementFeesMember_3ea43ba0-0969-4880-8ce0-467e4293f64a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeesMember_660e5cae-63ca-4b81-868b-4cd410e89b2a" xlink:href="alx-20210930.xsd#alx_DevelopmentFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:to="loc_alx_DevelopmentFeesMember_660e5cae-63ca-4b81-868b-4cd410e89b2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeasingFeesMember_29c30e7e-5566-4f16-8cc4-6c5648b2fcb7" xlink:href="alx-20210930.xsd#alx_LeasingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:to="loc_alx_LeasingFeesMember_29c30e7e-5566-4f16-8cc4-6c5648b2fcb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CommissionOnSaleOfRealEstateMember_f049803c-8c0c-4efa-9123-3dcf17b8dac4" xlink:href="alx-20210930.xsd#alx_CommissionOnSaleOfRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:to="loc_alx_CommissionOnSaleOfRealEstateMember_f049803c-8c0c-4efa-9123-3dcf17b8dac4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeesMember_6e832ac6-5a6a-470d-9068-122768d91384" xlink:href="alx-20210930.xsd#alx_PropertyManagementFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_38953a53-240c-4874-8ec2-035d6389418f" xlink:to="loc_alx_PropertyManagementFeesMember_6e832ac6-5a6a-470d-9068-122768d91384" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f56f9621-521f-47a3-b8eb-730d8f219888" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_05b0f607-e71a-46f1-9c3a-736390452248" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f56f9621-521f-47a3-b8eb-730d8f219888" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_f56f9621-521f-47a3-b8eb-730d8f219888_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f56f9621-521f-47a3-b8eb-730d8f219888" xlink:to="loc_us-gaap_RelatedPartyDomain_f56f9621-521f-47a3-b8eb-730d8f219888_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_2852f113-e873-4ba0-ad6d-c3dd00c2df3f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f56f9621-521f-47a3-b8eb-730d8f219888" xlink:to="loc_us-gaap_RelatedPartyDomain_2852f113-e873-4ba0-ad6d-c3dd00c2df3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_9c7e5b14-b90b-49e8-85cf-3b5d2b580cb4" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2852f113-e873-4ba0-ad6d-c3dd00c2df3f" xlink:to="loc_srt_AffiliatedEntityMember_9c7e5b14-b90b-49e8-85cf-3b5d2b580cb4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/MarketableSecuritiesAdditionalInformationDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#MarketableSecuritiesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MarketableSecuritiesAdditionalInformationDetail" xlink:type="extended" id="i6d71a39958af4fc7b8834f4621f6aebd_MarketableSecuritiesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentHoldingsLineItems_cab2ea65-9bb3-46a7-8ddb-e3de0ef2835d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentHoldingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_3be0a14a-b115-4116-81cd-71699bfa5d03" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_cab2ea65-9bb3-46a7-8ddb-e3de0ef2835d" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_3be0a14a-b115-4116-81cd-71699bfa5d03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecurities_bc92131f-d713-4ec9-9521-7cd336d80607" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_cab2ea65-9bb3-46a7-8ddb-e3de0ef2835d" xlink:to="loc_us-gaap_MarketableSecurities_bc92131f-d713-4ec9-9521-7cd336d80607" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_372ba715-4cbf-45ea-b193-7565afe5626b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_cab2ea65-9bb3-46a7-8ddb-e3de0ef2835d" xlink:to="loc_us-gaap_SharePrice_372ba715-4cbf-45ea-b193-7565afe5626b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentHoldingsTable_5656d2b0-787b-4cb1-a647-d15dbc0f3d60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentHoldingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InvestmentHoldingsLineItems_cab2ea65-9bb3-46a7-8ddb-e3de0ef2835d" xlink:to="loc_us-gaap_InvestmentHoldingsTable_5656d2b0-787b-4cb1-a647-d15dbc0f3d60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_9d4eea00-d50f-4707-8bd2-5c71c69e0feb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_5656d2b0-787b-4cb1-a647-d15dbc0f3d60" xlink:to="loc_us-gaap_InvestmentTypeAxis_9d4eea00-d50f-4707-8bd2-5c71c69e0feb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_9d4eea00-d50f-4707-8bd2-5c71c69e0feb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_9d4eea00-d50f-4707-8bd2-5c71c69e0feb" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_9d4eea00-d50f-4707-8bd2-5c71c69e0feb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_9e502724-6a75-41e3-a4a8-bd7a1c3f2675" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_9d4eea00-d50f-4707-8bd2-5c71c69e0feb" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_9e502724-6a75-41e3-a4a8-bd7a1c3f2675" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_9bad806e-5680-4865-b440-5758d71542be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_9e502724-6a75-41e3-a4a8-bd7a1c3f2675" xlink:to="loc_us-gaap_CommonStockMember_9bad806e-5680-4865-b440-5758d71542be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_53ec78f4-aec8-48df-a2e4-cf247256d3a5" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_5656d2b0-787b-4cb1-a647-d15dbc0f3d60" xlink:to="loc_dei_LegalEntityAxis_53ec78f4-aec8-48df-a2e4-cf247256d3a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_53ec78f4-aec8-48df-a2e4-cf247256d3a5_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_53ec78f4-aec8-48df-a2e4-cf247256d3a5" xlink:to="loc_dei_EntityDomain_53ec78f4-aec8-48df-a2e4-cf247256d3a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_37953ede-ec09-4224-adf2-d27238b016de" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_53ec78f4-aec8-48df-a2e4-cf247256d3a5" xlink:to="loc_dei_EntityDomain_37953ede-ec09-4224-adf2-d27238b016de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_MacerichMember_454ea263-5450-4e2f-82c7-27be4cb2ca02" xlink:href="alx-20210930.xsd#alx_MacerichMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_37953ede-ec09-4224-adf2-d27238b016de" xlink:to="loc_alx_MacerichMember_454ea263-5450-4e2f-82c7-27be4cb2ca02" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableSummaryofOutstandingMortgagesPayableDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#MortgagesPayableSummaryofOutstandingMortgagesPayableDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableSummaryofOutstandingMortgagesPayableDetail" xlink:type="extended" id="ia4fd33dcf3254f38999a09574f5af0e0_MortgagesPayableSummaryofOutstandingMortgagesPayableDetail">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_39b178cd-afb6-45ab-80b9-a3237879a268" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentMaturityDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_39b178cd-afb6-45ab-80b9-a3237879a268" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_2c886787-a8ca-4b52-8d10-7e3c86a88fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_2c886787-a8ca-4b52-8d10-7e3c86a88fc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NotesPayableGross_173752e0-e331-4a29-bc3f-7a761a781534" xlink:href="alx-20210930.xsd#alx_NotesPayableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_alx_NotesPayableGross_173752e0-e331-4a29-bc3f-7a761a781534" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_3ae6e523-ed75-4ff2-921a-39662fe4cf1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_3ae6e523-ed75-4ff2-921a-39662fe4cf1e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_bfb48511-9e4d-47df-a148-21a8dad07fbf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_us-gaap_NotesPayable_bfb48511-9e4d-47df-a148-21a8dad07fbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_d58d434b-29c0-4a01-8f1c-2603e5e94c02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_d58d434b-29c0-4a01-8f1c-2603e5e94c02" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_193fd31b-f793-44b8-a79a-3daae6406500" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_4377e38f-3c9b-4236-b398-bcf4b3554efe" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_193fd31b-f793-44b8-a79a-3daae6406500" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_177f6e21-0dec-460d-bed1-af5d1cf5bc2d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_193fd31b-f793-44b8-a79a-3daae6406500" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_177f6e21-0dec-460d-bed1-af5d1cf5bc2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_177f6e21-0dec-460d-bed1-af5d1cf5bc2d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_177f6e21-0dec-460d-bed1-af5d1cf5bc2d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_177f6e21-0dec-460d-bed1-af5d1cf5bc2d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_842dafcd-07b7-4dac-a073-db0792268e40" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_177f6e21-0dec-460d-bed1-af5d1cf5bc2d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_842dafcd-07b7-4dac-a073-db0792268e40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_bf275578-d727-461d-8bd2-c37908a55eb0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_842dafcd-07b7-4dac-a073-db0792268e40" xlink:to="loc_us-gaap_MortgagesMember_bf275578-d727-461d-8bd2-c37908a55eb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_da6c1300-6a85-4177-87c9-4371ea058c8f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_193fd31b-f793-44b8-a79a-3daae6406500" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_da6c1300-6a85-4177-87c9-4371ea058c8f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_da6c1300-6a85-4177-87c9-4371ea058c8f_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_da6c1300-6a85-4177-87c9-4371ea058c8f" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_da6c1300-6a85-4177-87c9-4371ea058c8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_da6c1300-6a85-4177-87c9-4371ea058c8f" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ParamusPropertyMember_7eadbe46-4bf0-48f5-9f9d-5059d8efad5b" xlink:href="alx-20210930.xsd#alx_ParamusPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:to="loc_alx_ParamusPropertyMember_7eadbe46-4bf0-48f5-9f9d-5059d8efad5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_00c84870-4b4e-4b54-9360-e8b9eaa8e2e2" xlink:href="alx-20210930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:to="loc_alx_LexingtonAvenuePropertyMember_00c84870-4b4e-4b54-9360-e8b9eaa8e2e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoPark2PropertyMember_6ffd27cd-2dbe-47db-a572-42ad2bea8368" xlink:href="alx-20210930.xsd#alx_RegoPark2PropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:to="loc_alx_RegoPark2PropertyMember_6ffd27cd-2dbe-47db-a572-42ad2bea8368" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AlexanderApartmentTowerMember_06d6a11e-5e71-4ba4-bf50-d4569a30950f" xlink:href="alx-20210930.xsd#alx_AlexanderApartmentTowerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_d7499dcb-b8b9-4be7-ae25-608de6359e00" xlink:to="loc_alx_AlexanderApartmentTowerMember_06d6a11e-5e71-4ba4-bf50-d4569a30950f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_f6debc36-3495-445f-a7a2-1410bf0660d7" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_193fd31b-f793-44b8-a79a-3daae6406500" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_f6debc36-3495-445f-a7a2-1410bf0660d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_f6debc36-3495-445f-a7a2-1410bf0660d7_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_f6debc36-3495-445f-a7a2-1410bf0660d7" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_f6debc36-3495-445f-a7a2-1410bf0660d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_6d10583d-1a15-43a0-a9e4-2f04e04ea7b9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_f6debc36-3495-445f-a7a2-1410bf0660d7" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_6d10583d-1a15-43a0-a9e4-2f04e04ea7b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OfficeBuildingMember_f295de6a-58a9-49b0-b6ae-26b08289ee12" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OfficeBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_6d10583d-1a15-43a0-a9e4-2f04e04ea7b9" xlink:to="loc_srt_OfficeBuildingMember_f295de6a-58a9-49b0-b6ae-26b08289ee12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_c5ea54cc-fa21-4e1d-ae15-a6144abbff3f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_6d10583d-1a15-43a0-a9e4-2f04e04ea7b9" xlink:to="loc_srt_RetailSiteMember_c5ea54cc-fa21-4e1d-ae15-a6144abbff3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ApartmentBuildingMember_7b44553d-0d29-4c75-97c9-9347ff9b69ac" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ApartmentBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_6d10583d-1a15-43a0-a9e4-2f04e04ea7b9" xlink:to="loc_srt_ApartmentBuildingMember_7b44553d-0d29-4c75-97c9-9347ff9b69ac" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableAdditionalInformationDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#MortgagesPayableAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableAdditionalInformationDetail" xlink:type="extended" id="if9098985f7dc4b09a57b15f1ff82361e_MortgagesPayableAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_14a7ae29-348a-445b-b95d-11e4d54ac523" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_14a7ae29-348a-445b-b95d-11e4d54ac523" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_a737436c-ea3f-4d45-a7cc-e0f13fa659f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_a737436c-ea3f-4d45-a7cc-e0f13fa659f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_91c44a63-ec7d-4010-91cd-ddd4e3c38daa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_91c44a63-ec7d-4010-91cd-ddd4e3c38daa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_0c57c99e-d38d-40d3-ad33-6990d1b019f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_us-gaap_NotesPayable_0c57c99e-d38d-40d3-ad33-6990d1b019f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount_191f57d3-9afc-46bf-8813-542aceb5c3ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_us-gaap_ParticipatingMortgageLoansParticipationLiabilitiesAmount_191f57d3-9afc-46bf-8813-542aceb5c3ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_07464186-b247-4de0-a071-7dfdb46e3e75" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_d031d649-db3b-4636-ac02-3054456ea16d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_us-gaap_TypeOfArrangementAxis_d031d649-db3b-4636-ac02-3054456ea16d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_d031d649-db3b-4636-ac02-3054456ea16d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_d031d649-db3b-4636-ac02-3054456ea16d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_d031d649-db3b-4636-ac02-3054456ea16d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_136a74b3-bed2-45b0-a096-29df0db5f766" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_d031d649-db3b-4636-ac02-3054456ea16d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_136a74b3-bed2-45b0-a096-29df0db5f766" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ParticipationAgreementMember_0eac9490-9612-48a2-9eac-199f6d61f58a" xlink:href="alx-20210930.xsd#alx_ParticipationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_136a74b3-bed2-45b0-a096-29df0db5f766" xlink:to="loc_alx_ParticipationAgreementMember_0eac9490-9612-48a2-9eac-199f6d61f58a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_245581fc-f362-477c-87a5-7775d52d1f56" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_245581fc-f362-477c-87a5-7775d52d1f56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_245581fc-f362-477c-87a5-7775d52d1f56_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_245581fc-f362-477c-87a5-7775d52d1f56" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_245581fc-f362-477c-87a5-7775d52d1f56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_934652a2-fb0f-4d36-b44e-b8864e5738bb" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_245581fc-f362-477c-87a5-7775d52d1f56" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_934652a2-fb0f-4d36-b44e-b8864e5738bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_45c15e56-ce27-4de7-8c95-992cd78474ec" xlink:href="alx-20210930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_934652a2-fb0f-4d36-b44e-b8864e5738bb" xlink:to="loc_alx_LexingtonAvenuePropertyMember_45c15e56-ce27-4de7-8c95-992cd78474ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoPark2PropertyMember_ae53629b-0b3f-4665-b808-ee1995469b70" xlink:href="alx-20210930.xsd#alx_RegoPark2PropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_934652a2-fb0f-4d36-b44e-b8864e5738bb" xlink:to="loc_alx_RegoPark2PropertyMember_ae53629b-0b3f-4665-b808-ee1995469b70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_861d0176-9323-4478-a1de-46151de7dbe7" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_861d0176-9323-4478-a1de-46151de7dbe7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_861d0176-9323-4478-a1de-46151de7dbe7_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_861d0176-9323-4478-a1de-46151de7dbe7" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_861d0176-9323-4478-a1de-46151de7dbe7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_2c9da1e0-81a5-420d-b1bc-0f1fcbdc231f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_861d0176-9323-4478-a1de-46151de7dbe7" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_2c9da1e0-81a5-420d-b1bc-0f1fcbdc231f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OfficeBuildingMember_d93c88c7-d7f7-442c-b527-5f4fec822440" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_OfficeBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_2c9da1e0-81a5-420d-b1bc-0f1fcbdc231f" xlink:to="loc_srt_OfficeBuildingMember_d93c88c7-d7f7-442c-b527-5f4fec822440" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_f7cfb239-ea13-43e5-84d5-84d74469fbd7" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_2c9da1e0-81a5-420d-b1bc-0f1fcbdc231f" xlink:to="loc_srt_RetailSiteMember_f7cfb239-ea13-43e5-84d5-84d74469fbd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_1a2ec08e-1442-44f9-92b6-51ea8725de86" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_1a2ec08e-1442-44f9-92b6-51ea8725de86" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_1a2ec08e-1442-44f9-92b6-51ea8725de86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_1a2ec08e-1442-44f9-92b6-51ea8725de86" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_1a2ec08e-1442-44f9-92b6-51ea8725de86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_482cbf4e-26e2-4497-bc59-60356a15c4e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_1a2ec08e-1442-44f9-92b6-51ea8725de86" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_482cbf4e-26e2-4497-bc59-60356a15c4e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_cb38b993-9b3f-423e-bd79-f316d5d1ab8a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_482cbf4e-26e2-4497-bc59-60356a15c4e4" xlink:to="loc_us-gaap_MortgagesMember_cb38b993-9b3f-423e-bd79-f316d5d1ab8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_0e725378-fb3a-47c5-aac2-279482b46168" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_us-gaap_VariableRateAxis_0e725378-fb3a-47c5-aac2-279482b46168" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_0e725378-fb3a-47c5-aac2-279482b46168_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_0e725378-fb3a-47c5-aac2-279482b46168" xlink:to="loc_us-gaap_VariableRateDomain_0e725378-fb3a-47c5-aac2-279482b46168_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_233a82dd-9e6f-4c5b-9e06-c1e16f49b51e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_0e725378-fb3a-47c5-aac2-279482b46168" xlink:to="loc_us-gaap_VariableRateDomain_233a82dd-9e6f-4c5b-9e06-c1e16f49b51e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_6aebdd18-0c79-4aa8-9826-9b029fc4ffdb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_233a82dd-9e6f-4c5b-9e06-c1e16f49b51e" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_6aebdd18-0c79-4aa8-9826-9b029fc4ffdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_d4e321b8-32f6-4df3-9238-9a4464300ca3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_4b24675e-ca68-42a6-b41a-940802c9bb20" xlink:to="loc_us-gaap_FinancialInstrumentAxis_d4e321b8-32f6-4df3-9238-9a4464300ca3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d4e321b8-32f6-4df3-9238-9a4464300ca3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_d4e321b8-32f6-4df3-9238-9a4464300ca3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d4e321b8-32f6-4df3-9238-9a4464300ca3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fc3f3a1e-3c08-4270-9fe3-abb7b2747fff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_d4e321b8-32f6-4df3-9238-9a4464300ca3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fc3f3a1e-3c08-4270-9fe3-abb7b2747fff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_3cfea4df-62ad-46d0-97ac-9a261c84d6c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fc3f3a1e-3c08-4270-9fe3-abb7b2747fff" xlink:to="loc_us-gaap_InterestRateSwapMember_3cfea4df-62ad-46d0-97ac-9a261c84d6c8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#StockBasedCompensationAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:type="extended" id="ia5588ec013b04127914f4a09b3dd6372_StockBasedCompensationAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_b273f1c3-ccb8-439c-a5b5-9842ca5da856" xlink:href="alx-20210930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_b273f1c3-ccb8-439c-a5b5-9842ca5da856" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_2de6c798-69c3-49e1-b06d-a75fd3f24137" xlink:href="alx-20210930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_2de6c798-69c3-49e1-b06d-a75fd3f24137" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_bec372cd-d99e-4da3-a96e-ca4d8c7fc656" xlink:href="alx-20210930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_bec372cd-d99e-4da3-a96e-ca4d8c7fc656" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValue_8efd0bc9-25d9-4ff2-87f2-64e6ed5c19e3" xlink:href="alx-20210930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValue_8efd0bc9-25d9-4ff2-87f2-64e6ed5c19e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_e1397186-d831-4a35-9c91-ffd5f2693935" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_e1397186-d831-4a35-9c91-ffd5f2693935" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_feae49da-ac58-4332-9c99-fca26b068c4b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_feae49da-ac58-4332-9c99-fca26b068c4b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_fd3580da-fd70-4c8a-8c59-0631041a8b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78688f7f-1124-4c33-83bb-de3a9052a2d4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_fd3580da-fd70-4c8a-8c59-0631041a8b9a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_f889fbfa-545d-4df1-8f6b-8d0db80505bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_fd3580da-fd70-4c8a-8c59-0631041a8b9a" xlink:to="loc_us-gaap_PlanNameAxis_f889fbfa-545d-4df1-8f6b-8d0db80505bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f889fbfa-545d-4df1-8f6b-8d0db80505bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_f889fbfa-545d-4df1-8f6b-8d0db80505bf" xlink:to="loc_us-gaap_PlanNameDomain_f889fbfa-545d-4df1-8f6b-8d0db80505bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_9daf4568-6074-480c-bab5-c8511f50037e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_f889fbfa-545d-4df1-8f6b-8d0db80505bf" xlink:to="loc_us-gaap_PlanNameDomain_9daf4568-6074-480c-bab5-c8511f50037e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_A2016OmnibusStockPlanMember_34645d43-c445-4a6b-a7d7-8c8b6d092d61" xlink:href="alx-20210930.xsd#alx_A2016OmnibusStockPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_9daf4568-6074-480c-bab5-c8511f50037e" xlink:to="loc_alx_A2016OmnibusStockPlanMember_34645d43-c445-4a6b-a7d7-8c8b6d092d61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_e1c8de51-ceaf-417a-beaa-0071f9ca2a32" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_fd3580da-fd70-4c8a-8c59-0631041a8b9a" xlink:to="loc_srt_TitleOfIndividualAxis_e1c8de51-ceaf-417a-beaa-0071f9ca2a32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e1c8de51-ceaf-417a-beaa-0071f9ca2a32_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_e1c8de51-ceaf-417a-beaa-0071f9ca2a32" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e1c8de51-ceaf-417a-beaa-0071f9ca2a32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_b47f6a86-61e8-4dbf-9e64-d27bc1e38032" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_e1c8de51-ceaf-417a-beaa-0071f9ca2a32" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_b47f6a86-61e8-4dbf-9e64-d27bc1e38032" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_ff015ca6-7399-4b03-8cbc-671c7e028455" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_b47f6a86-61e8-4dbf-9e64-d27bc1e38032" xlink:to="loc_srt_DirectorMember_ff015ca6-7399-4b03-8cbc-671c7e028455" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_58790957-ed36-40d3-8460-48cec4e34702" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_fd3580da-fd70-4c8a-8c59-0631041a8b9a" xlink:to="loc_us-gaap_AwardTypeAxis_58790957-ed36-40d3-8460-48cec4e34702" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58790957-ed36-40d3-8460-48cec4e34702_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_58790957-ed36-40d3-8460-48cec4e34702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58790957-ed36-40d3-8460-48cec4e34702_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_688fc0e8-6be1-4f47-b259-c07a13da99f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_58790957-ed36-40d3-8460-48cec4e34702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_688fc0e8-6be1-4f47-b259-c07a13da99f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DeferredStockUnitsMember_72716484-545d-4268-9a52-90811ab59766" xlink:href="alx-20210930.xsd#alx_DeferredStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_688fc0e8-6be1-4f47-b259-c07a13da99f2" xlink:to="loc_alx_DeferredStockUnitsMember_72716484-545d-4268-9a52-90811ab59766" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="extended" id="i9522a9d4e8524bc9ae9312a8a31953e8_FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8b5f89d-29c7-46dd-b41f-31f7fe42e2f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_f804e1e5-f0b3-4dfa-97bf-524bb8d89c1d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8b5f89d-29c7-46dd-b41f-31f7fe42e2f4" xlink:to="loc_us-gaap_AssetsAbstract_f804e1e5-f0b3-4dfa-97bf-524bb8d89c1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_e998b2b7-fd3a-45fa-83e9-34a0e2eb3735" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_f804e1e5-f0b3-4dfa-97bf-524bb8d89c1d" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_e998b2b7-fd3a-45fa-83e9-34a0e2eb3735" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_5a2b78cc-9e75-4a50-8573-c03fc59940a5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8b5f89d-29c7-46dd-b41f-31f7fe42e2f4" xlink:to="loc_us-gaap_LiabilitiesAbstract_5a2b78cc-9e75-4a50-8573-c03fc59940a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_6be0bddc-bf21-4ea5-be78-d1aafbd0ee79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_5a2b78cc-9e75-4a50-8573-c03fc59940a5" xlink:to="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_6be0bddc-bf21-4ea5-be78-d1aafbd0ee79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b0fba08e-8984-4491-aa56-5fcf0760f025" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8b5f89d-29c7-46dd-b41f-31f7fe42e2f4" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b0fba08e-8984-4491-aa56-5fcf0760f025" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e30f4a6c-de7f-4d67-95db-06d501b64575" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b0fba08e-8984-4491-aa56-5fcf0760f025" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e30f4a6c-de7f-4d67-95db-06d501b64575" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_e30f4a6c-de7f-4d67-95db-06d501b64575_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e30f4a6c-de7f-4d67-95db-06d501b64575" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_e30f4a6c-de7f-4d67-95db-06d501b64575_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_1ec25f3d-457d-411e-814b-3a8c8e5db493" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e30f4a6c-de7f-4d67-95db-06d501b64575" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_1ec25f3d-457d-411e-814b-3a8c8e5db493" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_b26af010-8de6-47ab-bc0f-a9edc688e5ca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_1ec25f3d-457d-411e-814b-3a8c8e5db493" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_b26af010-8de6-47ab-bc0f-a9edc688e5ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bcde95a4-837d-41a0-b095-5d031c3ee415" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b0fba08e-8984-4491-aa56-5fcf0760f025" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bcde95a4-837d-41a0-b095-5d031c3ee415" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bcde95a4-837d-41a0-b095-5d031c3ee415_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bcde95a4-837d-41a0-b095-5d031c3ee415" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bcde95a4-837d-41a0-b095-5d031c3ee415_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_13f21738-19ec-42dd-961c-65158f155f36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bcde95a4-837d-41a0-b095-5d031c3ee415" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_13f21738-19ec-42dd-961c-65158f155f36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_8fbbbb51-c495-4197-b3cc-1d067f975b5c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_13f21738-19ec-42dd-961c-65158f155f36" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_8fbbbb51-c495-4197-b3cc-1d067f975b5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_aa2582f2-e3b9-49ae-abee-1164ea01eda7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_13f21738-19ec-42dd-961c-65158f155f36" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_aa2582f2-e3b9-49ae-abee-1164ea01eda7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_6ba11a40-f4ce-4e30-b243-2cb0b50210e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_13f21738-19ec-42dd-961c-65158f155f36" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_6ba11a40-f4ce-4e30-b243-2cb0b50210e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_f5a788a5-a110-47f3-8969-9456a2ac2a47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b0fba08e-8984-4491-aa56-5fcf0760f025" xlink:to="loc_us-gaap_FinancialInstrumentAxis_f5a788a5-a110-47f3-8969-9456a2ac2a47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f5a788a5-a110-47f3-8969-9456a2ac2a47_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f5a788a5-a110-47f3-8969-9456a2ac2a47" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f5a788a5-a110-47f3-8969-9456a2ac2a47_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7552fd57-ea17-467f-b2e1-5409a2b12ce7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f5a788a5-a110-47f3-8969-9456a2ac2a47" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7552fd57-ea17-467f-b2e1-5409a2b12ce7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesAssetsMember_d00d3bb2-1dc6-414e-8ade-68dc5fff71eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuritiesAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7552fd57-ea17-467f-b2e1-5409a2b12ce7" xlink:to="loc_us-gaap_SecuritiesAssetsMember_d00d3bb2-1dc6-414e-8ade-68dc5fff71eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_3ebe055a-ade7-472e-a4cf-f72b1ad91757" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7552fd57-ea17-467f-b2e1-5409a2b12ce7" xlink:to="loc_us-gaap_InterestRateSwapMember_3ebe055a-ade7-472e-a4cf-f72b1ad91757" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesNotMeasuredatFairValueDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#FairValueMeasurementsFinancialAssetsandLiabilitiesNotMeasuredatFairValueDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesNotMeasuredatFairValueDetail" xlink:type="extended" id="ibee28cf77e614ee78b6772d98a01cda8_FairValueMeasurementsFinancialAssetsandLiabilitiesNotMeasuredatFairValueDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_36e4b782-d6d6-4bf7-b16a-cff0710a3143" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_8ace7b63-5b04-4a53-ab48-beee72153e5b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_36e4b782-d6d6-4bf7-b16a-cff0710a3143" xlink:to="loc_us-gaap_AssetsAbstract_8ace7b63-5b04-4a53-ab48-beee72153e5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_d0de3ffa-130c-45e5-b381-e19eb1a9e9aa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8ace7b63-5b04-4a53-ab48-beee72153e5b" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_d0de3ffa-130c-45e5-b381-e19eb1a9e9aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_8bce4130-1bfd-4e10-a174-30e5a0bfb23c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_36e4b782-d6d6-4bf7-b16a-cff0710a3143" xlink:to="loc_us-gaap_LiabilitiesAbstract_8bce4130-1bfd-4e10-a174-30e5a0bfb23c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableFairValueDisclosure_bf7984a1-911a-4fa2-996d-df7d9e0e3a64" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NotesPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_8bce4130-1bfd-4e10-a174-30e5a0bfb23c" xlink:to="loc_us-gaap_NotesPayableFairValueDisclosure_bf7984a1-911a-4fa2-996d-df7d9e0e3a64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_51ac2f33-5dd1-420f-96bb-67471b2931b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_36e4b782-d6d6-4bf7-b16a-cff0710a3143" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_51ac2f33-5dd1-420f-96bb-67471b2931b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_5ac94a26-0a26-456d-a167-effdec74c5f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_51ac2f33-5dd1-420f-96bb-67471b2931b4" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_5ac94a26-0a26-456d-a167-effdec74c5f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_5ac94a26-0a26-456d-a167-effdec74c5f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_5ac94a26-0a26-456d-a167-effdec74c5f7" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_5ac94a26-0a26-456d-a167-effdec74c5f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fc793e81-666b-4028-b337-3748d7c1f9f0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_5ac94a26-0a26-456d-a167-effdec74c5f7" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fc793e81-666b-4028-b337-3748d7c1f9f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_3cf23913-d9e7-4fcd-80b5-4da2f6def498" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fc793e81-666b-4028-b337-3748d7c1f9f0" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_3cf23913-d9e7-4fcd-80b5-4da2f6def498" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_9967da6e-0078-4665-a45e-7692d5ee81c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fc793e81-666b-4028-b337-3748d7c1f9f0" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_9967da6e-0078-4665-a45e-7692d5ee81c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_d481a2d0-697a-4e3f-bd66-295e2b28b690" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fc793e81-666b-4028-b337-3748d7c1f9f0" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_d481a2d0-697a-4e3f-bd66-295e2b28b690" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8dac4607-f5c0-4841-8bca-668554ae7d34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_51ac2f33-5dd1-420f-96bb-67471b2931b4" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8dac4607-f5c0-4841-8bca-668554ae7d34" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8dac4607-f5c0-4841-8bca-668554ae7d34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8dac4607-f5c0-4841-8bca-668554ae7d34" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8dac4607-f5c0-4841-8bca-668554ae7d34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_96c7b411-73ee-406e-8a01-47389335b0ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8dac4607-f5c0-4841-8bca-668554ae7d34" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_96c7b411-73ee-406e-8a01-47389335b0ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_e091a9dd-2f22-4c26-b880-327b49a79969" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_96c7b411-73ee-406e-8a01-47389335b0ba" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_e091a9dd-2f22-4c26-b880-327b49a79969" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_d06fcdcd-9d02-4cfe-b533-dbf0d0a87ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_96c7b411-73ee-406e-8a01-47389335b0ba" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_d06fcdcd-9d02-4cfe-b533-dbf0d0a87ce6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="simple" xlink:href="alx-20210930.xsd#CommitmentsandContingenciesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="extended" id="i9d51bfd1f0a746f4af854460f8a4b191_CommitmentsandContingenciesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoveragePerIncident_d315a684-b305-46fa-8af6-ddd8f2c2816a" xlink:href="alx-20210930.xsd#alx_InsuranceMaximumCoveragePerIncident"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_InsuranceMaximumCoveragePerIncident_d315a684-b305-46fa-8af6-ddd8f2c2816a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoveragePerProperty_3743238c-9acc-4fab-b544-1b7852401340" xlink:href="alx-20210930.xsd#alx_InsuranceMaximumCoveragePerProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_InsuranceMaximumCoveragePerProperty_3743238c-9acc-4fab-b544-1b7852401340" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoverageInAggregate_64aca28a-8358-42d3-9bf1-a5e926b5e6db" xlink:href="alx-20210930.xsd#alx_InsuranceMaximumCoverageInAggregate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_InsuranceMaximumCoverageInAggregate_64aca28a-8358-42d3-9bf1-a5e926b5e6db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceDeductible_ecea4db1-fce5-4cb6-a778-63ebaaa1a502" xlink:href="alx-20210930.xsd#alx_InsuranceDeductible"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_InsuranceDeductible_ecea4db1-fce5-4cb6-a778-63ebaaa1a502" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_SelfInsuredResponsibility_8e3aac91-02f8-4079-9ef0-90cccf984fcc" xlink:href="alx-20210930.xsd#alx_SelfInsuredResponsibility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_SelfInsuredResponsibility_8e3aac91-02f8-4079-9ef0-90cccf984fcc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_FederalGovernmentResponsibility_a1cfb554-aaaa-441f-abb7-d3f5dba079b8" xlink:href="alx-20210930.xsd#alx_FederalGovernmentResponsibility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_FederalGovernmentResponsibility_a1cfb554-aaaa-441f-abb7-d3f5dba079b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_66b001d1-a241-496a-860b-2f1e0da6d01c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AreaOfRealEstateProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_66b001d1-a241-496a-860b-2f1e0da6d01c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NumberOfFires_58fce406-1082-46bc-97d2-549b590ecf26" xlink:href="alx-20210930.xsd#alx_NumberOfFires"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_alx_NumberOfFires_58fce406-1082-46bc-97d2-549b590ecf26" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyDamagesSoughtValue_ed07b7a4-8f38-485b-8d7c-424cb14de6c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyDamagesSoughtValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_us-gaap_LossContingencyDamagesSoughtValue_ed07b7a4-8f38-485b-8d7c-424cb14de6c4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_c26bcd82-1755-42d0-b208-e579255db178" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_c26bcd82-1755-42d0-b208-e579255db178" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_3228f03c-b1a7-45fb-8de5-fbbf2cc8fe47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_3228f03c-b1a7-45fb-8de5-fbbf2cc8fe47" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_d79cb77b-d5c8-4443-94ca-ecf9724000c1" xlink:to="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_34871aad-7268-4bcf-ab06-708ba6d309fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_34871aad-7268-4bcf-ab06-708ba6d309fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_34871aad-7268-4bcf-ab06-708ba6d309fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_34871aad-7268-4bcf-ab06-708ba6d309fe" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_34871aad-7268-4bcf-ab06-708ba6d309fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_7f8881b0-431c-48a9-a87c-6996c1e87de3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_34871aad-7268-4bcf-ab06-708ba6d309fe" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_7f8881b0-431c-48a9-a87c-6996c1e87de3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralLiabilityMember_b344c3e5-c841-4e96-b494-d3d117a37546" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeneralLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeAndTierIdentifierDomain_7f8881b0-431c-48a9-a87c-6996c1e87de3" xlink:to="loc_us-gaap_GeneralLiabilityMember_b344c3e5-c841-4e96-b494-d3d117a37546" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DiseaseCoverageMember_bb318d52-def1-41ba-9740-7c2f4b9c832c" xlink:href="alx-20210930.xsd#alx_DiseaseCoverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeAndTierIdentifierDomain_7f8881b0-431c-48a9-a87c-6996c1e87de3" xlink:to="loc_alx_DiseaseCoverageMember_bb318d52-def1-41ba-9740-7c2f4b9c832c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_b357c249-117a-40e6-82b6-32fd1468fd5a" xlink:href="alx-20210930.xsd#alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_b357c249-117a-40e6-82b6-32fd1468fd5a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TypesAndTierIdentifierDomain_b357c249-117a-40e6-82b6-32fd1468fd5a_default" xlink:href="alx-20210930.xsd#alx_TypesAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_b357c249-117a-40e6-82b6-32fd1468fd5a" xlink:to="loc_alx_TypesAndTierIdentifierDomain_b357c249-117a-40e6-82b6-32fd1468fd5a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TypesAndTierIdentifierDomain_406f5a15-49bb-4bf9-840d-7ab41ca37e4a" xlink:href="alx-20210930.xsd#alx_TypesAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_b357c249-117a-40e6-82b6-32fd1468fd5a" xlink:to="loc_alx_TypesAndTierIdentifierDomain_406f5a15-49bb-4bf9-840d-7ab41ca37e4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AllRiskPropertyAndRentalValueMember_39c4c276-96bd-4167-a21e-4918bb86d673" xlink:href="alx-20210930.xsd#alx_AllRiskPropertyAndRentalValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_406f5a15-49bb-4bf9-840d-7ab41ca37e4a" xlink:to="loc_alx_AllRiskPropertyAndRentalValueMember_39c4c276-96bd-4167-a21e-4918bb86d673" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TerrorismCoverageIncludingNbcrMember_7f0bcacb-8011-40b2-ad57-1c2259a50867" xlink:href="alx-20210930.xsd#alx_TerrorismCoverageIncludingNbcrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_406f5a15-49bb-4bf9-840d-7ab41ca37e4a" xlink:to="loc_alx_TerrorismCoverageIncludingNbcrMember_7f0bcacb-8011-40b2-ad57-1c2259a50867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NbcrMember_7d61a726-9a48-4de9-ae54-35e1d8bc38d0" xlink:href="alx-20210930.xsd#alx_NbcrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_TypesAndTierIdentifierDomain_406f5a15-49bb-4bf9-840d-7ab41ca37e4a" xlink:to="loc_alx_NbcrMember_7d61a726-9a48-4de9-ae54-35e1d8bc38d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_dei_LegalEntityAxis_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa" xlink:to="loc_dei_EntityDomain_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_6b9718e3-6c5d-4792-9171-5146b580d567" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a17128a8-22c2-4bb3-9cf8-cd8c8b3094aa" xlink:to="loc_dei_EntityDomain_6b9718e3-6c5d-4792-9171-5146b580d567" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_3e934a7e-73e6-421a-acf3-0c74164f0e67" xlink:href="alx-20210930.xsd#alx_FiftyNinthStreetInsuranceCompanyLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6b9718e3-6c5d-4792-9171-5146b580d567" xlink:to="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_3e934a7e-73e6-421a-acf3-0c74164f0e67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_41ae331e-82ef-49f8-8981-e08fa091a387" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_41ae331e-82ef-49f8-8981-e08fa091a387" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_41ae331e-82ef-49f8-8981-e08fa091a387_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_41ae331e-82ef-49f8-8981-e08fa091a387" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_41ae331e-82ef-49f8-8981-e08fa091a387_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_ef1a009d-ff7b-49fc-9428-74cf1e96212d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_41ae331e-82ef-49f8-8981-e08fa091a387" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_ef1a009d-ff7b-49fc-9428-74cf1e96212d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoPark1PropertyMember_ce7c9ab1-98e5-4fb3-97fc-58958bbf6849" xlink:href="alx-20210930.xsd#alx_RegoPark1PropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_ef1a009d-ff7b-49fc-9428-74cf1e96212d" xlink:to="loc_alx_RegoPark1PropertyMember_ce7c9ab1-98e5-4fb3-97fc-58958bbf6849" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantAxis_86386df1-9452-424d-b30b-cb0a12678dfc" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_alx_RealEstatePropertyOccupantAxis_86386df1-9452-424d-b30b-cb0a12678dfc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_86386df1-9452-424d-b30b-cb0a12678dfc_default" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_86386df1-9452-424d-b30b-cb0a12678dfc" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_86386df1-9452-424d-b30b-cb0a12678dfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_3986f278-ab06-4a98-8e6e-89652210a29e" xlink:href="alx-20210930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_86386df1-9452-424d-b30b-cb0a12678dfc" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_3986f278-ab06-4a98-8e6e-89652210a29e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_SearsMember_77550f95-3145-4dc3-95b1-1e1789bf0914" xlink:href="alx-20210930.xsd#alx_SearsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_3986f278-ab06-4a98-8e6e-89652210a29e" xlink:to="loc_alx_SearsMember_77550f95-3145-4dc3-95b1-1e1789bf0914" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_8fa1c7f9-1672-4b8e-a970-711b39b2914b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_srt_RangeAxis_8fa1c7f9-1672-4b8e-a970-711b39b2914b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8fa1c7f9-1672-4b8e-a970-711b39b2914b_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_8fa1c7f9-1672-4b8e-a970-711b39b2914b" xlink:to="loc_srt_RangeMember_8fa1c7f9-1672-4b8e-a970-711b39b2914b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_24985993-f3d2-4e22-b3fa-26df5e89f58d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_8fa1c7f9-1672-4b8e-a970-711b39b2914b" xlink:to="loc_srt_RangeMember_24985993-f3d2-4e22-b3fa-26df5e89f58d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4bab57d7-805e-48be-a132-f349f167fe27" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_24985993-f3d2-4e22-b3fa-26df5e89f58d" xlink:to="loc_srt_MinimumMember_4bab57d7-805e-48be-a132-f349f167fe27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_16c01a08-aabb-4ed3-a9b1-199843c7bb11" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_24985993-f3d2-4e22-b3fa-26df5e89f58d" xlink:to="loc_srt_MaximumMember_16c01a08-aabb-4ed3-a9b1-199843c7bb11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_a7e6c79e-9d83-4ece-b29e-bab230aba239" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_efdcfc56-ee42-4630-ad1d-c3dd7eda99fd" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_a7e6c79e-9d83-4ece-b29e-bab230aba239" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_a7e6c79e-9d83-4ece-b29e-bab230aba239_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_a7e6c79e-9d83-4ece-b29e-bab230aba239" xlink:to="loc_us-gaap_LossContingencyNatureDomain_a7e6c79e-9d83-4ece-b29e-bab230aba239_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_114d04ae-bd06-4519-af7d-c3ae61de7f76" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_a7e6c79e-9d83-4ece-b29e-bab230aba239" xlink:to="loc_us-gaap_LossContingencyNatureDomain_114d04ae-bd06-4519-af7d-c3ae61de7f76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_EstimatedFutureDamagesMember_85ace990-2b82-42e0-8619-1928a88020c7" xlink:href="alx-20210930.xsd#alx_EstimatedFutureDamagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_114d04ae-bd06-4519-af7d-c3ae61de7f76" xlink:to="loc_alx_EstimatedFutureDamagesMember_85ace990-2b82-42e0-8619-1928a88020c7" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
