The Collaborative International Dictionary of English v.0.48:

Clapboard \Clap"board\, v. t.
   To cover with clapboards; as, to clapboard the sides of a
   house. [U. S.] --Bartlett.
   [1913 Webster] Clapbread

The Collaborative International Dictionary of English v.0.48:

Clapboard \Clap"board\, n.
   1. A narrow board, thicker at one edge than at the other; --
      used for weatherboarding the outside of houses. [U. S.]
      [1913 Webster]

   2. A stave for a cask. [Eng.] --Halliwell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

clapboard
    n 1: a long thin board with one edge thicker than the other;
         used as siding by lapping one board over the board below
         [syn: clapboard, weatherboard, weatherboarding]
    v 1: cover with clapboards

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "clapboard":
   Formica, Masonite, asphalt, beam, billet, blacktop, board,
   boarding, brick, canvas, carpeting, cobblestone, concrete, cord,
   cordwood, cork tile, deal, driftwood, fiber glass, firewood, flag,
   flagging, flagstone, flooring, hardwood, lath, lathing, lathwork,
   linoleum, log, lumber, macadam, panelboard, paneling, panelwork,
   pantile, paper, parquet, pavement, pavestone, paving, plank,
   planking, plasterboard, plyboard, plywood, pole, post, puncheon,
   roofage, roofing, roofing paper, shake, sheathing, sheathing board,
   sheeting, shingle, sideboard, siding, slab, slat, slate, softwood,
   splat, spun glass, stave, stick, stick of wood, stone, stovewood,
   tar paper, thatch, three-by-four, tile, tilestone, tiling, timber,
   timbering, timberwork, two-by-four, veneer, wainscoting, wallboard,
   walling, wallpaper, weatherboard, wood