hamburger bun vs hamburger roll

hamburger bun and hamburger roll both are nouns.

Word	Noun	Adjective	Verb	Adverb
hamburger bun	Yes	No	No	No
hamburger roll	Yes	No	No	No

As nouns, hamburger bun and hamburger roll are synonyms defined as:

hamburger bun and hamburger roll: a round bun shaped to hold a hamburger patty

hamburger bun (noun)	hamburger roll (noun)
a round bun shaped to hold a hamburger patty	a round bun shaped to hold a hamburger patty