Green’s Dictionary of Slang

1. (also grummit) the vagina.

1838		‘The Cadger’s Christening’ in Sparkling Songster 21: Peg Pullcock did loudly declare, / That she had the largest old grummit.
1888–94		‘Walter’ My Secret Life (1966) I 114: ‘You have been washing your grummet?’ No reply. [Ibid.] XI 2264: The other lad suddenly made a dig at the fair haired one’s clothes outside her grummit.
1890–1904		Farmer & Henley Sl. and Its Analogues.

2. sexual intercourse.

1984

Partridge DSUE (8th edn) : since mid-C.19.

3. (orig. N.Z. surfing, also grummit) a woman, esp. as a sex object.

1963

Morrieson Scarecrow 146: A sexy little piece like you is wasted on these hoboes [...]. Just wait till the boys see the class bit of grummit I’ve picked up for myself in the sticks.

4. (N.Z. juv., also grommet) someone or something disliked.

1984		informant in DNZE (1998).
1990		Dominion Sun. Times (Wellington) 22 Apr. 4: If you’re called [by adolescents] a grommet (a surfing term)...you’ve been insulted.