onion bread vs breadstuff

onion bread and breadstuff both are nouns.

Word	Noun	Adjective	Verb	Adverb
onion bread	Yes	No	No	No
breadstuff	Yes	No	No	No

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

onion bread: bread containing finely minced onions
breadstuff: food made from dough of flour or meal and usually raised with yeast or baking powder and then baked

Other hypernyms of onion bread include bread, staff of life.

onion bread (noun)	breadstuff (noun)
bread containing finely minced onions	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