knuckles vs brass knuckles

knuckles and brass knuckles both are nouns.

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

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

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

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

knuckles (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