acetanilide Syllabification: (ac·et·an·i·lide)Pronunciation: /ˌasiˈtanəˌlīd/Definition of acetanilide noun Chemistry a crystalline solid prepared by acetylation of aniline, used in dye manufacture. Chemical formula: C6H5NHCOCH3 Origin: mid 19th century: from acet(yl) + anil(ine) + -ideacetanilide in other Oxford dictionaries Definition of acetanilide in the British & World English dictionary