bun vs bread

bun and bread both are nouns.

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

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

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

Other hypernyms of bun include breadstuff, staff of life.

bun (noun)	bread (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
	informal terms for money

bun (verb)	bread (verb)
	cover with bread crumbs