gem vs bran muffin

gem and bran muffin both are nouns.

Word	Noun	Adjective	Verb	Adverb
gem	Yes	No	No	No
bran muffin	Yes	No	No	No

As nouns, bran muffin is a hyponym of gem; that is, bran muffin is a word with a more specific, narrower meaning than gem:

Other hyponyms of gem include corn muffin, popover.

gem (noun)	bran muffin (noun)
a precious or semiprecious stone incorporated into a piece of jewelry	muffin containing bran
art highly prized for its beauty or perfection
a sweet quick bread baked in a cup-shaped pan
a person who is as brilliant and precious as a piece of jewelry
a crystalline rock that can be cut and polished for jewelry