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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:fd2dd59d-50f1-480f-a752-7c7676a31568,g:404d10a4-e3ad-40cc-9488-2892f239161c-->
<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://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#PvpAdjustmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllAdjToCompMember" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#ecd_AllAdjToCompMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsReportedValueMember_97d64ce9-eefd-4cb1-a7bf-5a541bd89159" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsReportedValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsReportedValueMember_97d64ce9-eefd-4cb1-a7bf-5a541bd89159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsGrantedInCurrentYearMember_83a37bb1-663f-4eac-a351-5620ac59b835" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsGrantedInCurrentYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsGrantedInCurrentYearMember_83a37bb1-663f-4eac-a351-5620ac59b835" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsGrantedInPriorYearsUnvestedMember_17682f37-da70-4c54-9a62-0f990a92fa9f" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsGrantedInPriorYearsUnvestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsGrantedInPriorYearsUnvestedMember_17682f37-da70-4c54-9a62-0f990a92fa9f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsGrantedDuringTheYearVestedMember_fe9d6f22-d3b8-4380-936c-78521077dce8" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsGrantedDuringTheYearVestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsGrantedDuringTheYearVestedMember_fe9d6f22-d3b8-4380-936c-78521077dce8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsGrantedInPriorYearsVestedMember_49910277-6b7d-46d7-b09a-3c8b3571ff1d" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsGrantedInPriorYearsVestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsGrantedInPriorYearsVestedMember_49910277-6b7d-46d7-b09a-3c8b3571ff1d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsValueOfForfeitedAwardsAdjustmentMember_78700306-c83b-47d0-b375-2138582d7150" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsValueOfForfeitedAwardsAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsValueOfForfeitedAwardsAdjustmentMember_78700306-c83b-47d0-b375-2138582d7150" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_cswc_EquityAwardsValueOfDividendsAndOtherEarningsPaidAdjustmentMember_d92eeabd-607d-48a6-822a-0c984cfa7566" xlink:href="cswc-20240531.xsd#cswc_EquityAwardsValueOfDividendsAndOtherEarningsPaidAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cswc_EquityAwardsValueOfDividendsAndOtherEarningsPaidAdjustmentMember_d92eeabd-607d-48a6-822a-0c984cfa7566" xlink:type="arc" order="7"/>
  </link:definitionLink>
</link:linkbase>
