Green’s Dictionary of Slang

1. a mistress.

1675		Town-Misses Declaration 5: The Conveniency of Concubines was used in the very Primitive Ages.
1676		Etherege Man of Mode III iii: Dorimant’s convenient, Madam Lovett.
c.1698		B.E. Dict. Canting Crew.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 141: [He does not wish] to be thought, by his Companions, so unfashionable a Coxcomb as to want a female Conveniency.
1725		New Canting Dict. n.p.: conveniency, a Wife, also a Mistress.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1823		see sense 5.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1859		Matsell Vocabulum.
1895		Crowe Aus. Sl. Dict. 19: Convenient, a mistress.

2. (also convenient house) a brothel.

1675		Head Miss Display’d 121: [She will use] a Convenient House, standing in a Convenient Place, for the exercises of her deeds of darkness.
1708		N. Ward Mars Stript of his Armour 47: [Hit] over the Noddle with a Brace of Balls from a Place of Conveniency.
1761		Nancy Dawson’s Jests 11: One of those convenient houses, which is also an Inn on occasion.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 56: ‘Convenient (My)’ — a woman open to the speaker; if a landlady, her’s is ‘a very convenient house to call at.’.
1848		Sinks of London Laid Open 18: In short, this place, besides being a common lodging house, adds to it that now very necessary convenience — a brothel.

3. a prostitute.

1680		Character of a Town-Miss in C. Hindley Old Bk Collector’s Misc. 1: She [i.e. a whore] is an excellent Conveniency for those that have more Money than Wit.
1688		T. Shadwell Squire of Alsatia IV i: Oh, my pure blowen! my convenient! my tackle!
1696		Motteux (trans.) Pantagruelian Prognostications (1927) II 693: Those whom Venus is said to rule, as punks, [...] concubines, convenients, cracks, drabs.
c.1700		London-Bawd (1705) 76: Why, Madam, says he, I want a certain sort of a Fleshly Convenience.
1793		J. Caulfield Blackguardiana n.p.: Convenient, a mistress.

4. the vagina; thus, by metonymy, its possessor.

1683		Otway Atheist IV 350: I hate a new Conveniency that was never practised upon; ’tis like a new Shooe that was never worn, wrings and hurts one’s Foot basely and scurvily. I love me ease, I.
1707		N. Ward London Terraefilius V 27: The Coachman [...] can tell you which is furnish’d with the best Conveniency, the Dressing-Room or the Kitchen.

5. a wife.

c.1698		B.E. Dict. Canting Crew.
1720		C. Shadwell Irish Hospitality II i: How silly it is to be made an Angel before Marriage, and an humble Conveniency afterwards.

6. a lavatory.

1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.