(archaic, slang) A thief or pickpocket. / (slang, often in the plural) A knuckle duster.

plural of knuck

Any of the joints between the phalanges of the fingers. / (by extension) A mechanical joint. / A cut of meat.

(transitive) To apply pressure, or rub or massage with one's knuckles. / (transitive, slang) To strike or punch. / (intransitive) To bend the fingers.

(baseball) A pitch thrown with the ball gripped on the fingertips and released with no rotation, which travels over an unpredictable path to the plate due to micro-turbulence in the air.

(intransitive, baseball) To pitch knuckleballs.

(baseball slang) A knuckleball.

(intransitive, idiomatic) To get to work; to focus on a task. / To submit; knuckle under.

Alternative spelling of knuckle duster

(Britain, Australia) A weapon made of metal worn around the knuckles that strengthens the impact of a punch; brass knuckles.