the joint of a finger where it connects to the hand; the prominent bone that sticks out when you make a fist.
From Middle English 'knokel' or 'knuckle,' possibly from Old English 'cnucl' (bone), with roots in Germanic languages meaning 'small bone' or 'joint.'
Your knuckles crack when you stretch because gas bubbles in your joint fluid collapse—it's not bone breaking, but the sound is so distinctive that some people have addiction-like behaviors around cracking them, even though it won't give you arthritis.
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