The joint in the middle of your finger that sticks forward when you make a fist is an example of the knuckle.
- to rest the knuckles on the ground in shooting a marble
- to work energetically or seriously
- to yield; give in
Origin of knuckle
- Middle English knokel
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle English knokel (“finger joint”), ultimately from a diminutive of Proto-Germanic root *knuck- "bone". Cognate with Dutch knokkel (“knuckle”).