brass knuckles vs knucks

brass knuckles and knucks both are nouns.

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

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

brass knuckles and knucks: (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, knuckle duster, knuckles.

brass knuckles (noun)	knucks (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