Parker House roll vs bun

Parker House roll and bun both are nouns.

Word	Noun	Adjective	Verb	Adverb
Parker House roll	Yes	No	No	No
bun	Yes	No	No	No

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

Parker House roll: yeast-raised dinner roll made by folding a disk of dough before baking
bun: small rounded bread either plain or sweet

Other hypernyms of Parker House roll include roll.

Parker House roll (noun)	bun (noun)
yeast-raised dinner roll made by folding a disk of dough before baking	small rounded bread either plain or sweet