radiopaque dye vs dyestuff

radiopaque dye and dyestuff both are nouns.

Word	Noun	Adjective	Verb	Adverb
radiopaque dye	Yes	No	No	No
dyestuff	Yes	No	No	No

As nouns, dyestuff is a hypernym of radiopaque dye; that is, dyestuff is a word with a broader meaning than radiopaque dye:

radiopaque dye: dye that does not allow the passage of X rays or other radiation; used to outline certain organs during X-ray examination
dyestuff: a usually soluble substance for staining or coloring e.g. fabrics or hair

Other hypernyms of radiopaque dye include dye.

radiopaque dye (noun)	dyestuff (noun)
dye that does not allow the passage of X rays or other radiation; used to outline certain organs during X-ray examination	a usually soluble substance for staining or coloring e.g. fabrics or hair