(Chem.) A colorless, mobile, and very volatile liquid obtained from alcohol by certain processes of oxidation.
(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.