Green’s Dictionary of Slang

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

1938		cited in Partridge DSUE (1984) .
c.1943		S .J. Baker Aus. Vulgarisms [t/s] 10: growl: The female pudend. [...] Ex rhyming slang, growl and grunt.
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.

c.1943		S .J. Baker Aus. Vulgarisms [t/s] 10: growl: [...] 2. Coition. Ex rhyming slang, growl and grunt.
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.