Ground Floor

floor of a house or building on level with the ground

A storey (also spelled story), floor, deck or level is the level of a building above (or below) the ground. Buildings are often classified by how many levels they have. Low-rise, mid-rise, and high-rise buildings are all common, with the tallest skyscrapers having upwards of a hundred. Multi-storey buildings usually must have additional safety systems, such as fire sprinklers and fire escapes, as mandated by building codes.
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Noun
1. the floor of a building that is at or nearest to the level of the ground around the building
(synonym) first floor, ground level
(hypernym) floor, level, storey, story
2. becoming part of a venture at the beginning (regarded as position of advantage); "he got in on the ground floor"
(hypernym) beginning

Adjective
1. on the floor closest to level with the ground; "the ground-floor entrance is kept locked"
(similar) downstairs, downstair

the first stage of a new venture or investment opportunity.