knuckles

(noun) a small metal weapon; worn over the knuckles on the back of the hand. Synonyms: brass knucks, knucks, brass knuckles, knuckle duster.

(noun) a joint of a finger when the fist is closed. Synonyms: knuckle, knuckle joint, metacarpophalangeal joint.

(verb) press or rub with the knuckles. Synonyms: knuckle.

(verb) shoot a marble while keeping one's knuckles on the ground. Synonyms: knuckle.