Green’s Dictionary of Slang

1. to engage in lesbian sex, spec. the rubbing together of genitals.

1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 11: diking (it); used to refer to lesbian intercourse.
1972		B. Rodgers Queens’ Vernacular.
1993		(con. 1950s) Kennedy & Davies Boots of Leather (2014) 227: ‘What is dyking? It’s when a butch and a fem, the fem plays the woman part and the butch plays the male part, and the male lays on the female just like a man would do to a woman, except for there’s no intercourse [...] you don’t feel the penis inside you’.

2. to live as a lesbian.

1963

Kerouac letter 14 Jan. in Charters II (1999) 356: Here he is writhing in torment in Connecticutt-I-guess beds as she dikes ahead in Paree.