Definitions

1. noun

the joint or bony prominence at the base of the finger or toe

“The boxer’s swollen knuckle was visible to the audience.”

2. noun

the joint or bony part of the elbow, knee, or other parts of the body

“She rubbed the sore knuckle on her knee.”

3. verb

to hit or punch someone with the knuckles

“The kids knuckled each other in a playful fight.”