knuckle

(nŭkˈəl)

1. a. The prominence of the dorsal aspect of a joint of a finger, especially of one of the joints connecting the fingers to the hand.
   b. A rounded protuberance formed by the bones in a joint.
2. A cut of meat centering on the carpal or tarsal joint, as of a pig.
3. The part of a hinge through which the pin passes.
4. A sharp angle formed by the meeting of two surfaces, especially two ship's timbers.
5. knuckles Brass knuckles.

1. To press, rub, or hit with the knuckles.
2. To shoot (a marble) with the thumb over the bent forefinger.