Green’s Dictionary of Slang

(orig. US) the perineum, the space between the vagina and the anus.

1955		‘W. Baron’ Play This Love with Me 62: My prick was throbbing somewhere around her taint—you know what a woman's taint is: 'taint asshole and 'taint cunt [OED].
1971		E.E. Landy Underground Dict. (1972).
1972		B. Rodgers Queens’ Vernacular 194: tent (? fr t’ain’t = t’ain’t one or the other) area between the genitals and the anus.
1999		J. Stahl Perv (2001) 89: Two gingers’ width of dark between front and back, what Tennie used to call the ’taint (As in ‘’taint their ass and ’taint their pussy’).
2002		‘Touré’ Portable Promised Land (ms.) 62: I’d never heard ’tain’t used to refer to female anatomy — not the front door or the back door but a mysteriously alluring, unclassifiable, scary region between a woman’s legs (‘’Tain’t pussy and ’tain’t asshole, it’s just the tain’t,’ to quote Walter Bentley).
2005		Roger’s Profanisaurus in Viz Apr. 49: Them bits of skin that separtate cunts and arseholes. The taint, notcher, carse, snarse, biffin’s bridge, Humber Bridge, tinter etc.
2007		J. Stahl ‘Pure’ in Love Without 168: Thousands died for half an inch of taint.
2013		J. Stahl Happy Mutant Baby Pills 111: ‘You know about anogenital distance, right?’ [...] ‘Baby taint? Is that what we’re talking about?’.
2023		T. Pluck What Pluckery is This? 17 May 🌐 So, I cracked the frame of the Taint Hammer. (That’s my mountain bike.).