\Al"dol\, n. [Aldehyde + -ol as in alcohol.] (Chem.) A colorless liquid, {C4H8O2}, obtained by condensation of two molecules of acetaldehyde: CH3CHO + CH3CHO = H3CH(OH)CH2CO; also, any of various derivatives of this. The same reaction has been applied, under the name of {aldol condensation}, to the production of many compounds.