diapason vs diapason stop

diapason and diapason stop both are nouns.

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

As nouns, diapason and diapason stop are synonyms defined as:

diapason and diapason stop: either of the two main stops on a pipe organ

diapason (noun)	diapason stop (noun)
either of the two main stops on a pipe organ	either of the two main stops on a pipe organ