A venereal taint. He went out by Had’em, and came round by Clapham home; i.e. he went out a wenching, and got a clap.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Clanker * Clap on the ShoulderNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes