bomb vs explosive device

bomb and explosive device both are nouns.

Word	Noun	Adjective	Verb	Adverb
bomb	Yes	No	Yes	No
explosive device	Yes	No	No	No

As nouns, explosive device is a hypernym of bomb; that is, explosive device is a word with a broader meaning than bomb:

bomb: an explosive device fused to explode under specific conditions
explosive device: device that bursts with sudden violence from internal energy

Other hypernyms of bomb include arms, implements of war, munition, weaponry, weapons system.

bomb (noun)	explosive device (noun)
an explosive device fused to explode under specific conditions	device that bursts with sudden violence from internal energy
strong sealed vessel for measuring heat of combustion
an event that fails badly or is totally ineffectual

bomb (verb)	explosive device (verb)
throw bombs at or attack with bombs
fail to get a passing grade