Green’s Dictionary of Slang

(Us gay) adopting the passive or receptive role in anal intercourse or fist-fucking.

1960		Jrnl Social Therapy 171: If he is said to be ‘tops’, it means that he will assume only the active partnership in sodomy, while if he is called ‘tops or bottoms’, he will assume either the so-called male or female role in sodomy.
1973		D.Maurer ‘Criminal Narcotic Addict Sl.’ in Lang. Underworld (1981) 285/2: bottoms. A male homosexual who is the passive receptor in pederasty. Also sissy, stuff, sex punk, rap and bag it, queen pussy, boy girl.