acetyl Syllabification: (a·ce·tyl)Pronunciation: /əˈsētl, ˈasitl/Definition of acetyl noun [as modifier] Chemistry the acyl radical C(O)CH3, derived from acetic acid:acetyl chloride an acetyl groupOrigin: mid 19th century: from acetic + -ylacetyl in other Oxford dictionaries Definition of acetyl in the British & World English dictionary