grass roots vs plural form

grass roots and plural form both are nouns.

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

grass roots (noun)	plural form (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