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Webster 1913 Edition

Noun.

[

Lact

one +

ami

do.]

(Chem.)

One of a series of anhydrides of an amido type, analogous to the lactones, as oxindol; a cyclic amide.

lactam ‎(plural lactams)

(organic chemistry) Any of a class of cyclic amides, that are the nitrogen analogs of lactones, formed by heating amino acids; the tautomeric enol forms are known as lactims.

cyclic amides, nitrogen analogs of lactones

Greek prefixes indicate the ring size e.g. α- 3-membered, β- 4-membered.