bun vs breadstuff

bun and breadstuff both are nouns.

Word	Noun	Adjective	Verb	Adverb
bun	Yes	No	No	No
breadstuff	Yes	No	No	No

As nouns, breadstuff is a hypernym of bun; that is, breadstuff is a word with a broader meaning than bun:

bun: small rounded bread either plain or sweet
breadstuff: food made from dough of flour or meal and usually raised with yeast or baking powder and then baked

Other hypernyms of bun include bread, staff of life.

bun (noun)	breadstuff (noun)
small rounded bread either plain or sweet	food made from dough of flour or meal and usually raised with yeast or baking powder and then baked
	flour or meal or grain used in baking bread