The Collaborative International Dictionary of English v.0.48:

Fur \Fur\, v. t. [imp. & p. p. Furred; p. pr. & vb. n.
   Furring.]
   1. To line, face, or cover with fur; as, furred robes. "You
      fur your gloves with reason." --Shak.
      [1913 Webster]

   2. To cover with morbid matter, as the tongue.
      [1913 Webster]

   3. (Arch.) To nail small strips of board or larger scantling
      upon, in order to make a level surface for lathing or
      boarding, or to provide for a space or interval back of
      the plastered or boarded surface, as inside an outer wall,
      by way of protection against damp. --Gwill.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Furring \Fur"ring\, n.
   1. (Carp.)
      (a) The leveling of a surface, or the preparing of an air
          space, by means of strips of board or of larger
          pieces. See Fur, v. t., 3.
      (b) The strips thus laid on.
          [1913 Webster]

   2. (Shipbuilding) Double planking of a ship's side.
      [1913 Webster]

   3. A deposit from water, as on the inside of a boiler; also,
      the operation of cleaning away this deposit.
      [1913 Webster]

WordNet (r) 3.0 (2006):

furring
    n 1: a furlike coating of matter as on the tongue
    2: strip used to give a level surface for attaching wallboard
       [syn: furring strip, furring]