mumble-peg, n. — Green’s Dictionary of Slang

mumble-peg n.

also mumbledepeg

[SE mumble-the-peg; mumblety-peg, a game in which each player in turn throws a knife from a series of positions, continuing until they fail to make the blade stick in the ground]

the vagina.

a.1640		R. Brome New Academy II i: And she ha’ not good box and steel, I shall so grull her, And then at Mumbledepeg I will so firk her.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1964		B. Jackson Get Your Ass in the Water (1974) 148: There was Mumblepeg with a dick like a table peg, / her and her partner, Anna Funk.

In phrases

mumblepeg game, the (n.)

(US) sexual intercourse.

1856

Life in Boston & N.Y. (Boston, MA) 11 Oct. n.p.: Lid got rather miffed [...] and left, while the other two [girls] played at the mumblepeg game with the light out.