The Collaborative International Dictionary of English v.0.48:

Surbase \Sur"base`\, n. [Pref. sur- + base.]
   1. (Arch.) A cornice, or series of moldings, on the top of
      the base of a pedestal, podium, etc. See Illust. of
      Column.
      [1913 Webster]

   2. A board or group of moldings running round a room on a
      level with the tops of the chair backs. --Knight.
      [1913 Webster]

WordNet (r) 3.0 (2006):

surbase
    n 1: the molding or border above the base of a structure (a
         pedestal or podium or wall)