brass knuckles vs weapon system

brass knuckles and weapon system both are nouns.

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

As nouns, weapon system is a hypernym of brass knuckles; that is, weapon system is a word with a broader meaning than brass knuckles:

brass knuckles: (used in the plural) a small metal weapon; worn over the knuckles on the back of the hand
weapon system: any instrument or instrumentality used in fighting or hunting

Other hypernyms of brass knuckles include arm, weapon.

brass knuckles (noun)	weapon system (noun)
(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand	any instrument or instrumentality used in fighting or hunting