Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
semi-formal is an adjective meaning "moderately formal; requiring a dinner jacket". It carries one recorded sense.
moderately formal; requiring a dinner jacket
“he wore semiformal attire”
“a black-tie dinner”
Definitions, synonyms and semantic relations for semi-formal come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.