light arm vs weapon system

light arm and weapon system both are nouns.

Word	Noun	Adjective	Verb	Adverb
light arm	Yes	No	No	No
weapon system	Yes	No	No	No

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

light arm: a rifle or pistol
weapon system: any instrument or instrumentality used in fighting or hunting

Other hypernyms of light arm include arm, weapon.

light arm (noun)	weapon system (noun)
a rifle or pistol	any instrument or instrumentality used in fighting or hunting