Source : Webster's Revised Unabridged Dictionary (1913)

Formaldehyde \For*mal"de*hyde\, n. [Formic + aldehyde.] (Chem.)
   A colorless, volatile liquid, {H2CO}, resembling acetic or
   ethyl aldehyde, and chemically intermediate between methyl
   alcohol and formic acid.

Source : WordNet®

formaldehyde
     n : a colorless poisonous gas; made by the oxidation of methanol
         [syn: {methanal}]