noun Chemistry.
any of a group of cyclic amides characterized by the NHCO group, derived from aminocarboxylic acids by the intramolecular elimination of water from the amino and carboxylic groups.

1880–85; lact(one) + am(ide) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
lactam (ˈlæktæm)
chem any of a group of inner amides, derived from amino acids, having the characteristic group -CONH-
[C20: from lact(one) + am(ide)]

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American Heritage
Medical Dictionary

lactam lac·tam (lāk'tām')
An amide formed from amino carboxylic acids containing a keto group in a ring configuration, as seen in purines, pyrimidines, and antibiotics. It is tautomeric to lactim.

The American Heritage® Stedman's Medical Dictionary
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Example sentences
Beta-lactam antibiotics include penicillins, cephalosporins, and some newer medications.
These drugs get their name from the beta-lactam ring, the circular chemical structure that forms their business end.
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