Green’s Dictionary of Slang

nocturne n.

[joc. use of painting jargon nocturne, a night-piece]

a prostitute.

[UK]Farmer & Henley Sl. and Its Analogues.
[[US]Eble Campus Sl. Fall 6: nocturnal – of or pertaining to a prostitute [...] ‘Well, I’ve heard that she’s a little nocturnal’].