1. (noun)knuckle, knuckle joint, metacarpophalangeal joint a joint of a finger when the fist is closed Synonyms: metacarpophalangeal joint, knuckle joint, hinge joint, knuckle
2. (noun)knuckle joint, hinge joint a joint allowing movement in one plane only Synonyms: ginglymoid joint, metacarpophalangeal joint, ginglymus, knucklejoint, hinge joint, knuckle