parcel bomb vs bomb

parcel bomb and bomb both are nouns.

Word	Noun	Adjective	Verb	Adverb
parcel bomb	Yes	No	No	No
bomb	Yes	No	Yes	No

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

parcel bomb: a thin explosive device inside an envelope or package and detonated when opened
bomb: an explosive device fused to explode under specific conditions

parcel bomb (noun)	bomb (noun)
a thin explosive device inside an envelope or package and detonated when opened	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

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