The Collaborative International Dictionary of English v.0.48:

acetanilide \ac`et*an"i*lide\ ([a^]s`[e^]t*[a^]n"[i^]*l[i^]d),
   n. [Acetyl + anilide.] (Med., Chem.)
   An amide formed from aniline and an acetyl group
   (C6H5.NH.CO.CH3); it is a white crystalline compound used
   as an analgesic and also as an antipyretic. It has molecular
   weight 135.16. [Written also acetanilid] AS

   Syn: phenylacetamide, N-phenylacetamide, antifebrin,
        antifebrine, acetylaminobenzene, acetylaniline
        [1913 Webster + WordNet 1.5 + AS]

WordNet (r) 3.0 (2006):

acetanilide
    n 1: a white crystalline compound used as an analgesic and also
         as an antipyretic [syn: acetanilide, acetanilid,
         phenylacetamide]