necklace vs jewelry

necklace and jewelry both are nouns.

Word	Noun	Adjective	Verb	Adverb
necklace	Yes	No	No	No
jewelry	Yes	No	No	No

As nouns, jewelry is a hypernym of necklace; that is, jewelry is a word with a broader meaning than necklace:

necklace: jewelry consisting of a cord or chain (often bearing gems) worn about the neck as an ornament (especially by women)
jewelry: an adornment (as a bracelet or ring or necklace) made of precious metals and set with gems (or imitation gems)

Other hypernyms of necklace include jewellery.

necklace (noun)	jewelry (noun)
jewelry consisting of a cord or chain (often bearing gems) worn about the neck as an ornament (especially by women)	an adornment (as a bracelet or ring or necklace) made of precious metals and set with gems (or imitation gems)