Green’s Dictionary of Slang

1. (also groan and grunt, growl and grunt) the vagina.

1938		cited in Partridge DSUE (1984) .
a.1945		L. Payne private coll. n.p.: — Grumble & Grunt.
1969		S.T. Kendall Up the Frog.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 29: Growl and Grunt Vagina.
2002		R.G. Barrett Mystery Bay Blues 150: Despite the gigantic mumble on the grumble he gave her, there could be another [...] way to return the favour.

2. a generic term for women.

1956		J. Curtis Look Long Upon a Monkey 84: Potty having a grumble right here in the drum and letting it go to waste!
1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 148: A cruise, like. Plenty of grumble and grunt on those boats, innair?

3. (also groan and grunt, growl and grunt) sexual intercourse.

1966		Trimble 5000 Adult Sex Words and Phrases.
1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 169: Sorta thing blokes do, keep a little flat on the side for a bit of sparetime grumble.
1989		J. Morton Lowspeak.
2001		K. Sampson Outlaws (ms.) 105: It’s a well-known thing — the more I bevvy, the more I has to find me some grumble.