Source : Webster's Revised Unabridged Dictionary (1913)

Acyl \Ac"yl\, n. [Acid + -yl.] (Org. Chem.)
   An acid radical, as acetyl, malonyl, or benzoyl.

Source : WordNet®

acyl
     n : any group or radical of the form RCO- where R is an organic
         group; "an example of the acyl group is the acetyl group"
         [syn: {acyl group}]