knuckle

Your knuckles are the joints in your fingers that are farthest from your fingernails. When you clench your hand into a fist, your knuckles are especially prominent.

A knuckle is the part of your hand that makes it possible to move a finger freely, and if someone offers you a "knuckle sandwich," you should politely decline, since they're actually planning to make a fist and punch you in the mouth. To knuckle is to rub with the knuckles, like when you knuckle a bit of sand out of your eye. The root of knuckle is the Proto-Germanic knuk-, "bone."

Definitions of knuckle
1

n a joint of a finger when the fist is closed

Synonyms:
knuckle joint, metacarpophalangeal joint
Type of:
articulatio synovialis, diarthrosis, synovial joint
a joint so articulated as to move freely

v press or rub with the knuckles

Type of:
press
exert pressure or force to or upon

v shoot a marble while keeping one's knuckles on the ground

Type of:
shoot
throw or propel in a specific direction or towards a specific objective

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