Green’s Dictionary of Slang

a male homosexual.

1726		Weekly Journal, or The British Gazetteer 5 Mar. n.p.: A gang of Haunchmen, alias Endorsers, have likewise been taken up by the said Officers [...], some whereof have been committed to the Gatehouse.
1728		J. Dalton Narrative of Street-Robberies 34: As they were both dextrous at picking Pockets, they had better apply themselves to that, and leave these Indorsers to their beastly Appetites.
1739		State of Rome, under Nero and Domitian in 18C Erotica V n.p.: When T[histlethway]te both Sexes acts, before / A vile Indorser, and behind a Whore.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1890–1904		Farmer & Henley Sl. and Its Analogues.