Basement /(bāsment)/

Base·ment

Basement

n.
  1. The outer wall of the ground story of a building, or of a part of that story, when treated as a distinct substructure. (See Base, n., 3 (a).) Hence: The rooms of a ground floor, collectively. (Arch.)

Phrases & Compounds
Basement membrane
a delicate membrane composed of a single layer of flat cells, forming the substratum upon which, in many organs, the epithelioid cells are disposed.