organ stop vs diapason

organ stop and diapason both are nouns.

Word	Noun	Adjective	Verb	Adverb
organ stop	Yes	No	No	No
diapason	Yes	No	No	No

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

Other hyponyms of organ stop include diapason stop, dulciana, flue stop, reed stop, sourdine, voix celeste, vox angelica.

organ stop (noun)	diapason (noun)
a graduated set of organ pipes of like tone quality	either of the two main stops on a pipe organ