Green’s Dictionary of Slang

1. the penis.

1732-1820		Order of the Beggar's Benison and Merryland (1892) 31: Dinner Sentiments [...] ‘That’s a stunning affair,’ quoth the Damsel when she was hard pushed.
1748–49		Cleland Memoirs of a Woman of Pleasure (1985) 26: She [...] unbuttons his breeches, and removing his shirt, draws out his affair, so shrunk and diminish’d.
1770		D. Gunston (ed.) Jemmy Twitcher’s Jests 32: [S]eeing that the justice had got a very small affair in hand, she jeeringly said to him [etc].
1797		Bridges Burlesque Homer (4th edn) I 18: Besides, the wench does all things neatly, / And handles my affairs completely.
1870		Cythera’s Hymnal 44: Said he, ‘A man’s affair / Isn’t meant to go in there’.
1879		‘Lady Pokingham’ in Pearl 2 Aug. 18: Now’s the time, Alice, dear, my affair is so well greased, and your pussey is also ready.
1880		‘Sub-Umbra, or Sport among the She-Noodles’ in Pearl 7 Jan. 4: One by one she unfastened the buttons, then her soft delicate hand soon had possession of my stiff affair.
1898		Forbidden Fruit n.p.: She held my affair in her hand and slowly passed her fingers up and down.
1907		C. Prendergast Sadopaideia 23: You can’t feel Mr. Prendergast’s affair now, Juliette, it’s too busy; but he can feel your pussy quite well.

2. the vagina.

1762		Bridges Homer Travestie (1764) I 192: And all because that rogue on Ida, / Thought your affair a span too wide a.
1842		Wkly Rake (NY) 27 Aug. n.p.: Look out, or your head may be as horn-y as your lady’s other affair .
1879		‘Lady Pokingham’ in Pearl 3 Sept. 21: Kiss me, dear, I’m bursting to be into your tight little affair.
1901		More Forbidden Fruit 75: I placed Patty’s well-buttered affair over him for a ride.
1927		‘J.M. Hall’ Anecdota Americana I 136: When you get to bed tonight take his hand and put it on your affair.
1980		Maledicta IV:2 (Winter) 183: Examples here include [...] thing [...] affair.