Green’s Dictionary of Slang

a louse.

1788		Grose Classical Dict. of the Vulgar Tongue (2nd edn) n.p.: Gentleman’s companion. A louse.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Creepers. Gentlemen’s companions, lice.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

(W.I.) a euph. for gonorrhoea.

1927, 1943

cited in Cassidy & LePage Dict. Jam. Eng. (1980).

venereal disease.

1596		T. Lodge Wits Miserie IV 47: Tell him he hath ye pox, tut it is a gentlemens disease.
1675		Character of a Town-Gallant in C. Hindley Old Bk Collector’s Misc. 6: Cursing his Doctor for a Quacking Bastard, that understands a Gentleman’s Disease no more than a Farrier.

a highwayman.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Gentleman’s master, a highway robber, because he makes a gentleman obey his commands, i.e. stand and deliver.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1862		E. de la Bédollière Londres et les Anglais 314/2: gentleman’s master, voleur de grand chemin.

the vagina.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1980		Maledicta IV:2 (Winter) 182: Other references to function occur in [...] a Gentleman’s pleasure garden.