brass knuckles vs knuckle duster

brass knuckles and knuckle duster both are nouns.

Word	Noun	Adjective	Verb	Adverb
brass knuckles	Yes	No	No	No
knuckle duster	Yes	No	No	No

As nouns, brass knuckles and knuckle duster are synonyms defined as:

brass knuckles and knuckle duster: (used in the plural) a small metal weapon; worn over the knuckles on the back of the hand

Other synonyms of brass knuckles include brass knucks, knuckles, knucks.

brass knuckles (noun)	knuckle duster (noun)
(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand	(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand