Green’s Dictionary of Slang

quimsy n.

In phrases

have a bit of quimsy (v.) [quim n. (1)]

to have sexual intercourse.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 104: Encocher. To copulate; ‘to have a bit of quimsy’.