Green’s Dictionary of Slang

clap n.

also claps
[OF clapoir, bubo; thus clapoire or clapier, a place of debauchery and the illness one can contract there. The term appears as SE in late 16C but starts appearing in cant/slang lists in late 17C; Henke, Gutter Life and Language (1988) quotes Cotgrave’s definition (in Dict. French and English Tongues, 1611) of clapier as a rabbits’ nest (as well as a name for ‘old time Baudie houses’); thus a pun on SE coney, rabbit/cony n. (2a) – a man might catch the disease from a cony n. (2b) who was working in a clapoir]

[mid-16C+] venereal disease, esp. gonorrhoea.

In compounds

clap-clinic (n.)

[1970s+] a clinic specializing in venereal diseases.

clap-shack (n.)

[1940s] (US) a venereal disease clinic or hospital ward.

clap-trap (n.)

see separate entry.

SE in slang uses

In compounds

clap-shoulder (n.) [he claps a hand on one’s shoulder]

[17C] a bailiff or watchman.

clap-trap (n.)

see separate entry.

In phrases

clap on the shoulder (n.)

[17C–early 19C] an arrest for debt.