hydroxyl

from WordNet (r) 3.0 (2006)

hydroxyl
    n 1: the monovalent group -OH in such compounds as bases and
         some acids and alcohols [syn: {hydroxyl}, {hydroxyl group},
         {hydroxyl radical}]

from The Collaborative International Dictionary of English v.0.48

Hydroxyl \Hy*drox"yl\, n. [Hydro-, 2 + oxygen + -yl.] (Chem.)
   A compound radical, or unsaturated group, {HO}, consisting of
   one atom of hydrogen and one of oxygen. It is a
   characteristic part of the hydrates, the alcohols, the oxygen
   acids, etc.
   [1913 Webster]