Definition from Wiktionary, the free dictionary
knuckle (plural knuckles)
- Any of the joints between the phalanges of the fingers.
- (by extension) A mechanical joint.
- A cut of meat.
- (sports, billiards, snooker, pool) The curved part of the cushion at the entrance to the pockets on a cue sports table.
Derived terms 
Terms derived from “knuckle”
joint of the finger