Acyl
\Ac"yl\, n. [Acid + -yl.] (Org. Chem.) An acid radical, as acetyl, malonyl, or benzoyl. An acyl radical can be depicted as
R-CO-, where
-CO- is the carbonyl group, and R is the group that characterizes the acyl moiety.
[Webster 1913 Suppl. +PJC]