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2.
Belongs to the family of swear words that include parts of the human anatomy, such as 'shithead' and 'bitchface'.

It is both a noun and just a general expletive.
Voldemort: Harry, I killed your parents, and now I shall kill you. ~Struts towards Harry~
Harry: Just piss off you fuckerknuckle.

Emma: They're making 50 Shades of Grey into a film.
Hayley: Oh fuckerknuckle! Why?!!?
by Clairelikesapplejuice July 16, 2012
 
1.
In the game of marbles, the positioning of the clenched hand, with the thumb inverted into the clenched fingers, which propels a marble toward the target group of marbles. So called because of the hand resembling the common masturbation technique utilized by men, and because of the thumbs insertion into the "hole" resulting from the clenched position of the hand and fingers.
When I was a shorty, I was the Fucker Knuckle champion of the block.
by ken taylor January 02, 2005