amy-john, n. — Green’s Dictionary of Slang

amy-john n.

[play on SE Amazon + the comb. of male and female names; Wilson (1972) suggests Fr. ami Jean i.e. friend John]

a lesbian.

1965		Guild Dict. Homosexual Terms 22: homosexual (n.): One with a sexual attraction for those of the same sex who practices sex exclusively with those of the same sex. Related terms: amy-john.
1972		B. Rodgers Queens’ Vernacular.
1982		Maledicta VI:1+2 (Summer/Winter) 131: Check their completeness against this list if you will: amy-john (active lesbian, much rarer than dyke in general use).