onion roll vs bialy

onion roll and bialy both are nouns.

Word	Noun	Adjective	Verb	Adverb
onion roll	Yes	No	No	No
bialy	Yes	No	No	No

As nouns, bialy is a hyponym of onion roll; that is, bialy is a word with a more specific, narrower meaning than onion roll:

Other hyponyms of onion roll include bialystoker.

onion roll (noun)	bialy (noun)
yeast-raised roll flavored with onion	flat crusty-bottomed onion roll