gas bomb vs chemical weapon

gas bomb and chemical weapon both are nouns.

Word	Noun	Adjective	Verb	Adverb
gas bomb	Yes	No	No	No
chemical weapon	Yes	No	No	No

As nouns, chemical weapon is a hypernym of gas bomb; that is, chemical weapon is a word with a broader meaning than gas bomb:

gas bomb: a bomb laden with chemical agents that are released when the bomb explodes
chemical weapon: chemical substances that can be delivered using munitions and dispersal devices to cause death or severe harm to people and animals and plants

Other hypernyms of gas bomb include bomb.

gas bomb (noun)	chemical weapon (noun)
a bomb laden with chemical agents that are released when the bomb explodes	chemical substances that can be delivered using munitions and dispersal devices to cause death or severe harm to people and animals and plants