Green’s Dictionary of Slang

(orig. US) to fellate.

1971		‘T. Llewellyn’ Homosexual Love Let. 23: Lars, conscious of the fact that he would probably never get another opportunity to cock-suck Preben, took his time [Simes:DLSS].
1975		J. Carr Bad (1995) 44: What kinda work you in, boy? Cocksuckin’ or cornholin’?
1977		R. Hawkins Bimbos by the Bay (1998) 105: She cock-sucked him like crazy, and then he lost all control.
1998		‘Bill E. Goodhead’ Nubile Treat 🌐 He just couldn’t imagine how anything could possibly feel better than those lips of his mother’s on his tool. He was thrilled by the idea of being cock-sucked by his own Mom.