Green’s Dictionary of Slang

1. a female, esp. in the context of sexual intercourse.

1917		A.G. Empey Over the Top ‘Tommy’s Dict. of the Trenches’ 298: ‘Lonely Stab.’ A girl who writes and sends parcels to Tommy. She got his name from the ‘Lonely Soldier Column’ of some newspaper.
1966		Trimble 5000 Adult Sex Words and Phrases.

2. (Aus./US) sexual intercourse.

1950		Goldin et al. DAUL 206/2: Stab, n. 1. The act of copulation.
1952		W.R. Burnett Little Men, Big World 134: She put up with a lot from me at first. I was always seeing some cutie, and taking a stab.
1972		B. Rodgers Queens’ Vernacular 90: to fuck hard and fast [...] give one a stab (prison sl).