opaque gem vs gem

opaque gem and gem both are nouns.

Word	Noun	Adjective	Verb	Adverb
opaque gem	Yes	No	No	No
gem	Yes	No	No	No

As nouns, gem is a hypernym of opaque gem; that is, gem is a word with a broader meaning than opaque gem:

Other hypernyms of opaque gem include gemstone, stone.

opaque gem (noun)	gem (noun)
a gemstone that is opaque	a precious or semiprecious stone incorporated into a piece of jewelry
	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