C2H4O

Aldehyde Al"de*hyde ([a^]l"d[-e]*h[imac]d), n. [Abbrev. fr. alcohol dehydrogenatum, alcohol deprived of its hydrogen.] 1. (Chem.) A colorless, mobile, and very volatile liquid obtained from alcohol by certain processes of oxidation. [1913 Webster]

2. (Chem.) Any compound having the group {-CHO}. Methyl aldehyde, the simplest aldehyde, is more commonly called formaldehyde, {H-CHO}, and acetic aldehyde is now more commonly called {acetaldehyde}. The higher aldehydes may be solids. A {reducing sugar} typically contains the aldehyde group. [PJC]

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 {acetaldehyde}, {acetic aldehyde} or {ethyl aldehyde}), {C2H4O}; methyl aldehyde (called also {formaldehyde}), {CH2O}. [1913 Webster +PJC]

{Aldehyde ammonia} (Chem.), a compound formed by the union of aldehyde with ammonia. [1913 Webster]