noun
plural knuckles
[count] any one of the thick, bony parts (called joints) in your fingers
a piece of meat that includes a joint from the leg of an animal
a rap on/over/across the knuckles
rap (someone) on/over/across the knuckles
verb
knuckles; knuckled; knuckling
knuckle down
[phrasal verb] informal :to begin to work hard
knuckle under
[phrasal verb] informal :to stop trying to fight or resist something :to agree to do or accept something that you have been resisting or opposing
US