Source : Webster's Revised Unabridged Dictionary (1913)

Basement \Base"ment\, n. [F. soubassement. Of uncertain origin.
   Cf. {Base}, a., {Bastion}.] (Arch.)
   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.

   {Basement membrane} (Anat.), a delicate membrane composed of
      a single layer of flat cells, forming the substratum upon
      which, in many organs, the epithelioid cells are disposed.

Source : WordNet®

basement
     n 1: the lowermost portion of a structure partly or wholly below
          ground level; often used for storage [syn: {cellar}]
     2: the ground floor facade or interior in Renaissance
        architecture