Green’s Dictionary of Slang

to have sexual intercourse; thus firking school, a brothel or any place of unrestrained sexual frolics.

1600		Dekker Shoemakers’ Holiday IV i: In faith I would haue yearkt and firkt your Priscilla.
1610		Jonson Alchemist III iii: Firk, like a flounder; kiss, like a scallop, close: / And tickle him with thy mother-tongue.
a.1640		R. Brome New Academy II i: And she ha’ not good box and steel, I shall so grull her, And then at Mumbledepeg I will so firk her.
c.1642		T. Killigrew Parson’s Wedding (1664) I ii: If I had his heart-strings tied on a True-lover’s-knot, I would so firk him till he found physick in a Rope.
1647		‘Tom Nash his Ghost’ in Grosart Works of T. Nashe I (1883–4) lxix: I am a Ghost, and Ghosts doe feare no Lawes [...] I had a yerking, firking, jerking veine.
1663		Wandring Whore VI 5: [One] who had rather be firkt on the bare floor thin a Feather bed.
c.1670		Purgatorium Hibernicum 22: The more she strive to thrust him out / The more he firkt her hide about.
1672		Villiers Rehearsal V i: Like Maggots in Filberds, we’l snug in our shell, / We’l frisk in our shell, / We’l firk in our shell.
1682		‘Ballad’ in Wilson Court Satires of the Restoration (1976) 104: Bodmin blindfold knows the way / To her most secret place. / Her brother that he may be quits, / Firks Bodmin’s sister’s rump.
a.1700		‘Mistery Discovered’ in Chappell Roxburghe Ballads (1874) II 352: [She] would Firk it, Caper and jerk it, Though she seems cold in Carreses.
1710		J. Dunton ‘The He-Strumpets’ in Athenianism – Project IV 89: The Cracks will rave and think it much / If the New Sodomitish Crew / Han’t a brisk Firking Bout or two.
1863		in T.P. Lowry Stories the Soldiers Wouldn’t Tell (1994) 36: Tell Fred I want to know he get any nigger wench firking.
1960		in E. Cray Erotic Muse (1992) 97: The elders of the church, / They were too old to firk, / So they sat around the table / And had a circle jerk.