grassroots (Adjective) — Fundamental. ex. "the grassroots factor in making the decision"
grassroots (Adjective) — Of or involving the common people as constituting a fundamental political and economic group. ex. "a grassroots movement for nuclear disarmament"
grassroots (Noun) — The essential foundation or source. ex. "the problem was attacked at the grass roots"
grassroots (Noun) — The common people at a local level (as distinguished from the centres of political activity).