KNUCKLE (apparently the diminutive of a word for " bone," found in Ger. Knochen), the joint of a finger, which, when the hand is shut, is brought into prominence. In mechanical use the word is applied to the round projecting part of a hinge through which the pin is run, and in ship-building to an acute angle on some of the timbers. A " knuckle-duster," said to have originally come from the criminal slang of the United States, is a brass or metal instrument fitting on to the hand across the knuckles, with projecting studs and used for inflicting a brutal blow.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)