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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a09274-7362-77ce-817f-056817b87fc2,g:3207cb2d-0658-450d-85aa-2a46e48dc545-->
<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.carislifesciences.com/role/Cover" xlink:type="simple" xlink:href="cai-20260914.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.carislifesciences.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_01a09274-7362-7855-80f6-3fbb06348643" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_DocumentInformationTable_01a09274-7362-7855-80f6-3fbb06348643" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsExchangeAxis_01a09274-7362-77c5-b903-c3b2d72eb5ac" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityListingsExchangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_01a09274-7362-7855-80f6-3fbb06348643" xlink:to="loc_dei_EntityListingsExchangeAxis_01a09274-7362-77c5-b903-c3b2d72eb5ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_01a09274-7362-77c5-b903-c3b2d72eb5ac_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityListingsExchangeAxis_01a09274-7362-77c5-b903-c3b2d72eb5ac" xlink:to="loc_dei_ExchangeDomain_01a09274-7362-77c5-b903-c3b2d72eb5ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_01a09274-7362-77e9-a0de-639fdb2bac04" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityListingsExchangeAxis_01a09274-7362-77c5-b903-c3b2d72eb5ac" xlink:to="loc_dei_ExchangeDomain_01a09274-7362-77e9-a0de-639fdb2bac04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_exch_XNAS_01a09274-7362-703f-bed6-47221ad66033" xlink:href="https://xbrl.sec.gov/exch/2026/exch-2026.xsd#exch_XNAS"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_01a09274-7362-77e9-a0de-639fdb2bac04" xlink:to="loc_exch_XNAS_01a09274-7362-703f-bed6-47221ad66033" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_exch_XCHI_01a09274-7362-7862-bd46-cb10622d6bd5" xlink:href="https://xbrl.sec.gov/exch/2026/exch-2026.xsd#exch_XCHI"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_01a09274-7362-77e9-a0de-639fdb2bac04" xlink:to="loc_exch_XCHI_01a09274-7362-7862-bd46-cb10622d6bd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_01a09274-7362-7fa5-8c1f-33af22e349a6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_DocumentType_01a09274-7362-7fa5-8c1f-33af22e349a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_01a09274-7362-78cc-9e4a-2402927e25dd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_DocumentPeriodEndDate_01a09274-7362-78cc-9e4a-2402927e25dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_01a09274-7362-7d39-befb-b8ce38fac0fb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityRegistrantName_01a09274-7362-7d39-befb-b8ce38fac0fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a09274-7362-7dab-91ad-35200fa22391" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a09274-7362-7dab-91ad-35200fa22391" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a09274-7362-7daf-8e6e-6fc3b8e08706" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityFileNumber_01a09274-7362-7daf-8e6e-6fc3b8e08706" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a09274-7362-7d04-89de-e437ff49010f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a09274-7362-7d04-89de-e437ff49010f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_01a09274-7362-7975-b7d0-2f19e02edb8b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityAddressAddressLine1_01a09274-7362-7975-b7d0-2f19e02edb8b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_01a09274-7362-73b3-a064-deaab2679efa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityAddressAddressLine2_01a09274-7362-73b3-a064-deaab2679efa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_01a09274-7362-7075-9c06-3080014c617a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityAddressCityOrTown_01a09274-7362-7075-9c06-3080014c617a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_01a09274-7362-7a4f-bb47-3af065aff482" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityAddressStateOrProvince_01a09274-7362-7a4f-bb47-3af065aff482" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_01a09274-7362-7ade-ae63-4b157b8ee677" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityAddressPostalZipCode_01a09274-7362-7ade-ae63-4b157b8ee677" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_01a09274-7362-71e1-848a-84699b3df554" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_CityAreaCode_01a09274-7362-71e1-848a-84699b3df554" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_01a09274-7362-7a33-a151-c3358c159e11" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_LocalPhoneNumber_01a09274-7362-7a33-a151-c3358c159e11" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_01a09274-7362-7334-8ca7-6cc3aa15db64" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_WrittenCommunications_01a09274-7362-7334-8ca7-6cc3aa15db64" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_01a09274-7362-7b54-aa3a-e91d19f781e7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_SolicitingMaterial_01a09274-7362-7b54-aa3a-e91d19f781e7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_01a09274-7362-7b0b-959e-0f224243281d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_PreCommencementTenderOffer_01a09274-7362-7b0b-959e-0f224243281d" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_01a09274-7362-7cb8-abbd-56c6b1ed2fef" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_01a09274-7362-7cb8-abbd-56c6b1ed2fef" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_01a09274-7362-7e3e-862c-4fe80b38a339" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_Security12bTitle_01a09274-7362-7e3e-862c-4fe80b38a339" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_01a09274-7362-7067-a2b3-3546a6ee5a42" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_TradingSymbol_01a09274-7362-7067-a2b3-3546a6ee5a42" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_01a09274-7362-7d9c-848e-1d83a38660aa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_SecurityExchangeName_01a09274-7362-7d9c-848e-1d83a38660aa" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a09274-7362-7fb8-bca0-1497649d5942" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a09274-7362-7fb8-bca0-1497649d5942" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_01a09274-7362-7f3b-a733-f8d967f1def1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityExTransitionPeriod_01a09274-7362-7f3b-a733-f8d967f1def1" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a09274-7362-7072-a59b-da3e864cd36d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_EntityCentralIndexKey_01a09274-7362-7072-a59b-da3e864cd36d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a09274-7362-7a9c-8d37-e8dd26d0556b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a09274-7362-769f-a0dc-2a2d3558c5e2" xlink:to="loc_dei_AmendmentFlag_01a09274-7362-7a9c-8d37-e8dd26d0556b" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
