grass roots vs plural

grass roots and plural both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass roots	Yes	No	No	No
plural	Yes	Yes	No	No

grass roots (noun)	plural (noun)
the common people at a local level (as distinguished from the centers of political activity)	the form of a word that is used to denote more than one
the essential foundation or source

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