Same as nub, but, the G letter is actualy a 1337 typo wich originaly was: fucking nub, but the spacebar was pressed a bit too early and it ended up: fuckin gnub. Since "fuckin" is a legit 1337 way to spell fucking many people mistake gnub for a totaly new word.
So in short - gnub = fucking nub
STFU gnub! - the proper way.

U f00king gnub - dumbass way.
by Hazard October 30, 2004
A piece of hash that had been cunningly burned off before giving to the unknowing owner
Ah I see you took a nice gnub for yourself off my hash there you cheeky thing
by Cossymodo February 12, 2017