Hydroxy- \Hy*drox"y-\ (Chem.) A combining form, also used adjectively, indicating hydroxyl as an ingredient.

Hydroxy acid (Chem.), an organic acid, having (besides the hydroxyl group of the carboxyl radical) an alcoholic hydroxyl group, and thus having the qualities of an alcohol in addition to its acid properties; as, lactic and tartaric acids are hydroxy acids.

Source: Webster's Revised Unabridged Dictionary (1913)