caprolactamPronunciation: /ˌkaprə(ʊ)ˈlaktam/Definition of caprolactam noun [mass noun] Chemistry a synthetic crystalline compound which is an intermediate in nylon manufacture. A lactam; chemical formula: C6H11NO Origin: 1940s: from caproic acid + lactamcaprolactam in other Oxford dictionaries Definition of caprolactam in the US English dictionary