The term is based on the animal called a "zonkey", which is a cross between a zebra and a donkey.
P2: A zebra monkey hybrid?
P1: No you idiot, that's impossible-it's a zombie monkey!
P2: Oh shit, that God Damn Zonkey just bit me in the crotch!
2. the name given to any animal when one doesn't know its actual name.
Guy 1: "This is my first time at the zoo, what's that animal right there?"
Guy 2: "Yo, that's a zonkey, man."
Guy 1: "Damn, gotta get out the hood more."