Green’s Dictionary of Slang

fress v.

[Yid. fress, to eat; thus play on eat v. (4)]
(orig. US)

to perform either form of oral intercourse, usu. cunnilingus.

Show quotations
[US]L. Bruce Essential Lenny Bruce 43: He walked into the bathroom while she was ‘fressing the maid’. ‘Fressing‘ is Yiddish: it means eating.