Greek fire vs weapon

Greek fire and weapon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Greek fire	Yes	No	No	No
weapon	Yes	No	No	No

As nouns, weapon is a hypernym of Greek fire; that is, weapon is a word with a broader meaning than Greek fire:

Greek fire: a mixture used by Byzantine Greeks that was often shot at adversaries; catches fire when wetted
weapon: any instrument or instrumentality used in fighting or hunting

Other hypernyms of Greek fire include arm, weapon system, mixture.

Greek fire (noun)	weapon (noun)
a mixture used by Byzantine Greeks that was often shot at adversaries; catches fire when wetted	any instrument or instrumentality used in fighting or hunting
	a means of persuading or arguing