organ pipe vs flue

organ pipe and flue both are nouns.

Word	Noun	Adjective	Verb	Adverb
organ pipe	Yes	No	No	No
flue	Yes	No	No	No

As nouns, flue is a hyponym of organ pipe; that is, flue is a word with a more specific, narrower meaning than organ pipe:

organ pipe: the flues and stops on a pipe organ
flue: organ pipe whose tone is produced by air passing across the sharp edge of a fissure or lip

Other hyponyms of organ pipe include flue pipe, labial pipe, organ stop, reed pipe.

organ pipe (noun)	flue (noun)
the flues and stops on a pipe organ	a conduit to carry off smoke
	organ pipe whose tone is produced by air passing across the sharp edge of a fissure or lip
	flat bladelike projection on the arm of an anchor