Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
unendurable is an adjective meaning "incapable of being tolerated or endured". It carries one recorded sense.
incapable of being tolerated or endured
“an intolerable degree of sentimentality”
Definitions, synonyms and semantic relations for unendurable come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.