The Collaborative International Dictionary of English v.0.48:

Weather-board \Weath"er-board`\, v. t. (Arch.)
   To nail boards upon so as to lap one over another, in order
   to exclude rain, snow, etc. --Gwilt.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Weatherboard \Weath"er*board`\, n.
   1. (Naut.)
      (a) That side of a vessel which is toward the wind; the
          windward side.
      (b) A piece of plank placed in a porthole, or other
          opening, to keep out water.
          [1913 Webster]

   2.
      (a) (Arch.) A board extending from the ridge to the eaves
          along the slope of the gable, and forming a close
          junction between the shingling of a roof and the side
          of the building beneath.
      (b) A clapboard or feather-edged board used in
          weatherboarding.
          [1913 Webster]

WordNet (r) 3.0 (2006):

weatherboard
    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]
    2: the side toward the wind [syn: to windward, windward
       side, weatherboard, weather side]