pitch pipe vs pipe

pitch pipe and pipe both are nouns.

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

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

pitch pipe: a small pipe sounding a tone of standard frequency; used to establish the starting pitch for unaccompanied singing
pipe: a tubular wind instrument

pitch pipe (noun)	pipe (noun)
a small pipe sounding a tone of standard frequency; used to establish the starting pitch for unaccompanied singing	a long tube made of metal or plastic that is used to carry water or oil or gas etc.
	a tube with a small bowl at one end; used for smoking tobacco
	the flues and stops on a pipe organ
	a tubular wind instrument
	a hollow cylindrical shape