Source : Webster's Revised Unabridged Dictionary (1913)

Aldehyde \Al"de*hyde\, n. [Abbrev. fr. alcohol dehydrogenatum,
   alcohol deprived of its hydrogen.] (Chem.)
   A colorless, mobile, and very volatile liquid obtained from
   alcohol by certain processes of oxidation.

   Note: The aldehydes are intermediate between the alcohols and
         acids, and differ from the alcohols in having two less
         hydrogen atoms in the molecule, as common aldehyde
         (called also {acetic aldehyde} or {ethyl aldehyde}),
         {C2H4O}; methyl aldehyde, {CH2O}.

Source : WordNet®

aldehyde
     n : any of a class of highly reactive chemical compounds; used
         in making resins and dyes and organic acids