Green’s Dictionary of Slang

centrique part n.

the vagina.

[c.1706		Dutch Riddle 2/1: Tho’ seated at the lower End, / ’Tis always in the Middle found].
1788		Harris’s List of Covent-Garden Ladies 65: Pour down to the centrical point from every Cyprian spring a whole flood of liquid life.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 148: Gnomon, m. The female pudendum [...] ‘the centrique part’.
[1970		‘Troy Conway’ Cunning Linguist (1973) 123: She was [...] encased in a short black leather skirt which just did manage to cover her all-important dead centre].