Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
one-half is a noun meaning "one of two equal parts of a divisible whole". It carries one recorded sense.
one of two equal parts of a divisible whole
“half a loaf”
“half an hour”
“a century and one half”
Definitions, synonyms and semantic relations for one-half come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.