ETYM Old Eng. knokel, knokil, AS. cuncel; akin to Dutch knokkel, OFries. knokele, knokle, German knöchel, Swed. knoge, Dan. knokkel, German knochen bone, and perh. to Eng. knock.
A joint of a finger when the fist is closed; SYN. knuckle joint, metacarpophalangeal joint.

ETYM See Knuckle (n.).
1. To press or rub with the knuckles.
2. To shoot a marble while keeping one's knuckles on the ground.