plural vs undies

plural and undies both are nouns.

Word	Noun	Adjective	Verb	Adverb
plural	Yes	Yes	No	No
undies	Yes	No	No	No

plural (noun)	undies (noun)
the form of a word that is used to denote more than one	women's underwear

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