Green’s Dictionary of Slang

a male homosexual.

1828		‘Jon Bee’ Living Picture of London 159: He repeated the same offence in Westminster, was detected in flagrante delictu, but got off for a comparatively small sum [...] and betook himself off to Paris, the Boulevards among, – fit place for such a Jocelyn-monster.
2001		OnLine Dict. of Playground Sl. 🌐 Jocelyn, Jozlin n. derog. a homosexual.