Green’s Dictionary of Slang

cum v.

[often found, e.g. in written pornography, as an alternative to come v.1 ; the sp. enhances the sexual aspect of the otherwise common word]

to achieve orgasm.

[US] ‘Charlotte the Harlot’ in G. Logsdon Whorehouse Bells Were Ringing (1995) xviii: Way down on the prairie where cow plop is thick, / Where women are women and cowpokes cum quick.
[Aus](con. 1940s–60s) Hogbotel & ffuckes ‘A More Vulgar Mind’ in Snatches and Lays 46: She taught that young man to ejaculate, / A more vulgar mind would say cum.
[UK]Kirk & Madsen After The Ball 295: I’m going to cum.
[UK]Guardian 24 July 21: Was this the inspiration behind her famous catch phrase ‘Cum up and see me sometime’?
‘UK Snowy’ ‘Christmas Blackmail’ at [Internet] ‘I think I‘ve just cum Ian,’ she murmured in a real time little girl voice. ‘But it was cool. Have you cum?’.