plural vs crown jewels

plural and crown jewels both are nouns.

Word	Noun	Adjective	Verb	Adverb
plural	Yes	Yes	No	No
crown jewels	Yes	No	No	No

plural (noun)	crown jewels (noun)
the form of a word that is used to denote more than one	regalia (jewelry and other paraphernalia) worn by a sovereign on state occasions

plural (adjective)	crown jewels (adjective)
grammatical number category referring to two or more items or units
composed of more than one member, set, or kind