Green’s Dictionary of Slang

(US gay) a passive partner in a lesbian relationship.

1958		Murtagh & Harris Cast the First Stone 34: She was the head pop and all the other moms thought I was hot stuff to get her.
1967		S. Harris Hellhole 84: And, at Hudson, I gained a lot because I was Jerry’s mom.
1972		B. Rodgers Queens’ Vernacular.