acyl ac·yl (ās'əl)
A organic radical having the general formula RCO, derived from the removal of a hydroxyl group from an organic acid.
An organic compound containing the group RCO, where R is a halogen. Acyls are formed from organic acids by replacing the hydroxyl group (OH) within the carboxyl group (COOH) with a halogen. For example, acetyl chloride (CH3COCl) is formed by replacing the hydroxyl group of acetic acid (CH3COOH) with a chlorine atom. The names of acyls are formed by replacing the suffix -ic of the acid's name with -yl.