Knuckle

The knuckles are the joints of the fingers, which are brought into prominence when the hand is shut. The word is derived from the diminutive of a word for bone, found in German Knochen. Medically, it is said that the knuckles are formed by the metacarpophalangeal and interphalangeal joints of the finger. Knuckle-dusters or brass knuckles are said to have originally come from the criminal slang of the United States, and are brass or metal instrument fitting on to the hand across the knuckles, used to inflict a more brutal impact during a punch.