ground glass

from WordNet (r) 3.0 (2006)

ground glass
    n 1: glass that diffuses light due to a rough surface produced
         by abrasion or etching
    2: particulate glass made by grinding and used as an abrasive

from The Collaborative International Dictionary of English v.0.48

ground \ground\,
   imp. & p. p. of {Grind}.
   [1913 Webster]

   {ground cock}, a cock, the plug of which is ground into its
      seat, as distinguished from a compression cock. --Knight.

   {Ground glass}, glass the transparency of which has been
      destroyed by having its surface roughened by grinding.

   {Ground joint}, a close joint made by grinding together two
      pieces, as of metal with emery and oil, or of glass with
      fine sand and water.
      [1913 Webster]