- any one of a class of cyclic hydroxy-imides (enols) which can be tautomeric aided by the lactams.
- among a series of anhydrides resembling the lactams, but of an imido kind. Cf. lactam.
- The name of a course of organic substances containing the team -C(OH):N-. It is a tautomeric and, sometimes, isomeric kind of the lactam radical.