weapon vs weapon system

weapon and weapon system both are nouns.

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

As nouns, weapon and weapon system are synonyms defined as:

weapon and weapon system: any instrument or instrumentality used in fighting or hunting

Other synonyms of weapon include arm.

weapon (noun)	weapon system (noun)
any instrument or instrumentality used in fighting or hunting	any instrument or instrumentality used in fighting or hunting
a means of persuading or arguing