Green’s Dictionary of Slang

1. the vagina.

1888–94

‘Walter’ My Secret Life (1966) VIII 1666: Put your finger up my cu, cher.

2. a woman regarded as a sex object.

1960, 1975		Wentworth & Flexner DAS 125/1: cou n. A girl.
1962		J. Quirk No Red Ribbons (1968) 132: There’s one thing I haven’t got yet in Rome, and it’s spelled coo. [Ibid.] 214: I think I’ll marry that coo.

3. a derog. term of abuse.

1938		X. Herbert Capricornia (1939) 66: I’ll crack ye — big flash coo!
1986		P. Slabolepszy ‘Boo to the Moon’ Mooi Street (1994) 155: I been a real prick – sorry, I mean a real cu. I mean a ...