jewel vs emerald

jewel and emerald both are nouns.

Word	Noun	Adjective	Verb	Adverb
jewel	Yes	No	Yes	No
emerald	Yes	No	No	No

As nouns, emerald is a hyponym of jewel; that is, emerald is a word with a more specific, narrower meaning than jewel:

jewel: a precious or semiprecious stone incorporated into a piece of jewelry
emerald: a transparent piece of emerald that has been cut and polished and is valued as a precious gem

Other hyponyms of jewel include crown jewel, solitaire, diamond, ruby, pearl, sapphire.

jewel (noun)	emerald (noun)
a precious or semiprecious stone incorporated into a piece of jewelry	the green color of an emerald
a person who is as brilliant and precious as a piece of jewelry	a transparent piece of emerald that has been cut and polished and is valued as a precious gem
	a green transparent form of beryl; highly valued as a gemstone

jewel (verb)	emerald (verb)
adorn or decorate with precious stones