pipe bomb vs bomb

pipe bomb and bomb both are nouns.

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

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

pipe bomb (noun)	bomb (noun)
a small homemade bomb usually contained in a metal pipe	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

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