Source : Webster's Revised Unabridged Dictionary (1913)

Acetyl \Ac"e*tyl\, n. [L. acetum vinegar + Gr. ? substance. See
   {-yl}.] (Chem.)
   A complex, hypothetical radical, composed of two parts of
   carbon to three of hydrogen and one of oxygen. Its hydroxide
   is acetic acid.

Source : WordNet®

acetyl
     n : the organic group of acetic acid (CH3CO-) [syn: {acetyl
         group}, {acetyl radical}, {ethanoyl group}, {ethanoyl
         radical}]