knuckle duster vs brass knuckles

knuckle duster and brass knuckles both are nouns.

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

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

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

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

knuckle duster (noun)	brass knuckles (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