ground floor

(noun) the floor of a building that is at or nearest to the level of the ground around the building. Synonyms: ground floor, first floor, ground level.

(noun) becoming part of a venture at the beginning (regarded as position of advantage). Synonyms: ground floor. Example: "He got in on the ground floor."

(adj) on the floor closest to level with the ground. Synonyms: ground-floor. Example: "The ground-floor entrance is kept locked."