The Collaborative International Dictionary of English v.0.48:
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.
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
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.