azo dye vs dyestuff

azo dye and dyestuff both are nouns.

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

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

azo dye: any dye containing one or more azo groups
dyestuff: a usually soluble substance for staining or coloring e.g. fabrics or hair

Other hypernyms of azo dye include dye.

azo dye (noun)	dyestuff (noun)
any dye containing one or more azo groups	a usually soluble substance for staining or coloring e.g. fabrics or hair