Green’s Dictionary of Slang

1. (US) the vagina.

1934		H. Roth Call It Sleep (1977) 52: ‘Put yuh han’ in my knish,’ she coaxed. ‘Jus’ once.’.
1972		B. Rodgers Queens’ Vernacular 57: the female sex organ [...] knish.
1996		H. Roth From Bondage 391: Knish (vulgarism) cunt.

2. (US gay) the anus.

1949

‘Swasarnt Nerf’ et al. Gay Girl’s Guide 12: kanish: NYC MBS [Male Bobby-Soxer] term for ass-hole, used with ref. to anal intercourse.

3. a typical housewife on a gambling spree.

1968

T. Thackrey Gambling Secrets of Nick The Greek 107: This woman was a ‘knish’ – that is, she had the beginning spread, cast-iron hairdo, and overset rings of the typical housewife ‘on a little outing’ in Las Vegas.