The Collaborative International Dictionary of English v.0.48:

Hydroxide \Hy*drox"ide\, n. [Hydro-, 2 + oxide.] (Chem.)
   A hydrate; a substance containing hydrogen and oxygen, made
   by combining water with an oxide, and yielding water by
   elimination. The hydroxides are regarded as compounds of
   hydroxyl, united usually with basic element or radical; as,
   calcium hydroxide ethyl hydroxide.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hydroxide
    n 1: a compound of an oxide with water [syn: hydroxide,
         hydrated oxide]
    2: a chemical compound containing the hydroxyl group