the.com/knuckle
the hinge that lets you wave hello or threaten violence with the same hardware
means A finger joint, especially the rounded bony part on the back of the hand where a finger meets the palm.
from From late Middle English 'knokel,' meaning a small bone or joint — likely a diminutive built from the same Germanic stock that gave Dutch 'knokkel' and German 'Knöchel' (ankle, bone). It carried the general sense of any rounded knob of bone before the hand-joints won the word for themselves. The phrase 'knuckle down' comes from old marbles games, where you literally pressed your knuckles to the ground before a shot.
phantom soundcracking is gas bubbles bursting in joint fluid
old myth bustedcracking doesn't cause arthritis, studies confirm
word originoriginally meant any joint, including knees
brass versionbanned weapon in many states and countries
sandwich slanga knuckle sandwich is a punch to the mouth