IPA: //ˌʌn.səˈpɔː.tə.bəl//
KK: /ʌnˈsʌpɔrtəbl/
Something that cannot be supported or tolerated.
The claims made in the report were deemed unsupportable by the committee.
Unsupportable → It is formed from "un-" (meaning not) and "supportare" (from Latin, meaning to carry or bear). The word means not able to be carried or borne, indicating something that cannot be supported.
Think of 'not' ('un-') being able to 'carry' ('supportare') something — that's why unsupportable means something that cannot be supported.