atom-bomb vs bomb

atom-bomb is not a noun while bomb is a noun.

Word	Noun	Adjective	Verb	Adverb
atom-bomb	No	No	Yes	No
bomb	Yes	No	Yes	No

As verbs, bomb is a hypernym of atom-bomb; that is, bomb is a word with a broader meaning than atom-bomb:

Other hypernyms of atom-bomb include bombard.

atom-bomb (noun)	bomb (noun)
	an explosive device fused to explode under specific conditions
	strong sealed vessel for measuring heat of combustion
	an event that fails badly or is totally ineffectual

atom-bomb (verb)	bomb (verb)
bomb with atomic weapons	throw bombs at or attack with bombs
	fail to get a passing grade