Green’s Dictionary of Slang

venereal disease.

1665		G. Harvey Venus Unmasked 2: The Had’em [i.e. pox].
c.1698		B.E. Dict. Canting Crew n.p.: The Spark has been at Haddums, He is Clapt, or Poxt.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 16: But Noseless Sir, and snuffling Madam, / Since all had been alike at Hadem.
1725		New Canting Dict. [as cit. c.1698].
a.1731		N. Ward Wine Bibber’s Wish (in Miscellaneous Works IV 26): [She is] not a Stranger to the Sport; Nay, some will say She’s been at had ’em.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: He went out by Had’em, and came round by Clapham home; i.e. he went out a wenching, and got a clap. [Ibid.] He has been at Had’em, and came home by Clapham.
1811		Lex. Balatronicum [as cit. 1785].
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 134: ‘He’s been to Clapham,’ i.e. is indisposed, in a certain way.
1896		Farmer Vocabula Amatoria (1966) 20: Attraper quelque chose. To be ‘poxed’ or ‘clapped’; ‘to go by Clapham and come home by way of Had’em’.