grass roots vs foundation

grass roots and foundation both are nouns.

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

As nouns, foundation is a hypernym of grass roots; that is, foundation is a word with a broader meaning than grass roots:

grass roots (noun)	foundation (noun)
the common people at a local level (as distinguished from the centers of political activity)	the act of starting something for the first time; introducing something new
the essential foundation or source	lowest support of a structure
	a woman's undergarment worn to give shape to the contours of the body
	the fundamental assumptions from which something is begun or developed or calculated or explained
	education or instruction in the fundamentals of a field of knowledge
	an institution supported by an endowment
	the basis on which something is grounded