To have carnal knowledge of a woman; also to play badly on the harpsichord; or any other stringed instrument. A strummer of wire, a player on any instrument strung with wire.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Strum * StrumpetNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes