The Collaborative International Dictionary of English v.0.48:

Surface \Sur"face`\, n. [F. See Sur-, and Face, and cf.
   Superficial.]
   1. The exterior part of anything that has length and breadth;
      one of the limits that bound a solid, esp. the upper face;
      superficies; the outside; as, the surface of the earth;
      the surface of a diamond; the surface of the body.
      [1913 Webster]

            The bright surface of this ethereous mold. --Milton.
      [1913 Webster]

   2. Hence, outward or external appearance.
      [1913 Webster]

            Vain and weak understandings, which penetrate no
            deeper than the surface.              --V. Knox.
      [1913 Webster]

   3. (Geom.) A magnitude that has length and breadth without
      thickness; superficies; as, a plane surface; a spherical
      surface.
      [1913 Webster]

   4. (Fort.) That part of the side which is terminated by the
      flank prolonged, and the angle of the nearest bastion.
      --Stocqueler.
      [1913 Webster]

   Caustic surface, Heating surface, etc. See under
      Caustic, Heating, etc.

   Surface condensation, Surface condenser. See under
      Condensation, and Condenser.

   Surface gauge (Mach.), an instrument consisting of a
      standard having a flat base and carrying an adjustable
      pointer, for gauging the evenness of a surface or its
      height, or for marking a line parallel with a surface.

   Surface grub (Zool.), the larva of the great yellow
      underwing moth (Triphoena pronuba). It is often
      destructive to the roots of grasses and other plants.

   Surface plate (Mach.), a plate having an accurately dressed
      flat surface, used as a standard of flatness by which to
      test other surfaces.

   Surface printing, printing from a surface in relief, as
      from type, in distinction from plate printing, in which
      the ink is contained in engraved lines.
      [1913 Webster]

WordNet (r) 3.0 (2006):

surface gauge
    n 1: gauge consisting of a scriber mounted on an adjustable
         stand; used to test the accuracy of plane surfaces [syn:
         surface gauge, surface gage, scribing block]