a story of a building, partly or wholly underground.

(in classical and Renaissance architecture) the portion of a building beneath the principal story, treated as a single compositional unit.

the lowermost portion of a structure.

the substructure of a columnar or arched construction.

noun

attic

noun

bottom , cellar , crypt , excavation , furnace room , storage , substructure , subterranean room , underbuilding , understructure , vaultnotes:a cellar is a storage place , usually underground , for foodstuffs etc; basement is the lowest story of a building , part or wholly below ground level