Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
buttoned-up is an adjective meaning "(British colloquial) not inclined to conversation". It carries 2 recorded senses.
Definitions, synonyms and semantic relations for buttoned-up come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.