Green’s Dictionary of Slang

put n.2

[SE put, a card-game + pun on put, an act of thrusting or pushing and in 1. the vagina being ‘dark’; 2. SE two-handed, whole-hearted ]

In phrases

put in the dark (n.)

[late 17C] sexual intercourse.

two-handed put (n.)

[late 18C–19C] sexual intercourse.