Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
unthinkably is an adverb meaning "to an unimaginable extent". It carries one recorded sense.
to an unimaginable extent
Definitions, synonyms and semantic relations for unthinkably come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. .