A facial disfigurement. Someone who suffers from 'gloonkey' has a lower jaw that protrudes further than the upper jaw. The word is specifically defined so that if a sufferer pronounces it, their condition is expressed to the extreme due to the gurning involved, and thus other people who see it will understand the meaning on a visual basis.

(noun) A successful type of theft which results in an acceptable, impressive and rewarding payday for the protagonist.