Green’s Dictionary of Slang

turn n.2

[SE turn-up, a prostitute + turn, an act, a performance]

an act of sexual intercourse.

[UK]L. Barry Ram-Alley III i: But now a tweluepeny weekley Landress, Will serue the turne to halfe a dozen of them.
[UK]Massinger Bondman II ii: They haue made my Doctor too Phisitian to the Army, he was vs’de To serue the turn at a pinch: but I am now Quite vnprouided.
[UK]T. Killigrew Parson’s Wedding (1664) I ii: Him! marry, God bless all good women from him; why, he talks as if the Dairy-maid and all her Cows could not serve his turn.
[UK]Proceedings before his Highness Councel Concerning the Petitioners of the Isle of Ely against George Clapthorne Esqyure 27 Oct. 5: The said Roger Branham [...] heard one John Norman pleasant with the wife of William Martin profering her five shillings for a good turn.
[UK]Buckingham Chances IV iii: She is not for thy turn.
[UK]C. Deveureux Venus in India I 76: As I keep a pretty little piece of brown meat, and have my regular greens twice a week, I might not be able to do as good a turn now, as I did then, but I had that woman eight solid times, sir.
[UK]Farmer Vocabula Amatoria (1966) 82: Course, m. An act of coition; ‘a turn.’.
[Aus]J. Hibberd A Stretch of the Imagination (2000) 120: That’s when you discovered us. Stacked on a turn.
[UK]K. Waterhouse Soho 102: Does she – er – give a turn?

In phrases

do a turn (on one’s back) (v.) [for the woman to turn over onto her back + pun on theatrical use]

of a woman, to make herself available for sexual intercourse.

[UK]F. Norman in Fashion July in Norman’s London (1969) 254: Cor I bet she can’t arf do a turn!
[UK]F. Norman Too Many Crooks Spoil the Caper 77: She looked as though she might do a turn.
[US]Maledicta IV:2 (Winter) 182: The tendency [for vaginal fluid to flow] is also remembered in the phrases to [...] do, have or perform a bottom-wetter, namely to do a turn on one’s back.
[UK]J. Sullivan ‘To Hull and Back’ Only Fools and Horses [TV script] I reckon she’d do a turn if you played your cards right.
[UK]P. Baker Fabulosa 291/2: do a turn to have sex.