Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

hydroxy acid
     n : any acid that has hydroxyl groups in addition to the
         hydroxyl group in the acid itself