Source : Webster's Revised Unabridged Dictionary (1913)

Water line \Wa"ter line`\
   1. (Shipbuilding) Any one of certain lines of a vessel,
      model, or plan, parallel with the surface of the water at
      various heights from the keel.

   Note: In a half-breadth plan, the water lines are outward
         curves showing the horizontal form of the ship at their
         several heights; in a sheer plan, they are projected as
         straight horizontal lines.

   2. (Naut.) Any one of several lines marked upon the outside
      of a vessel, corresponding with the surface of the water
      when she is afloat on an even keel. The lowest line
      indicates the vessel's proper submergence when not loaded,
      and is called the {light water line}; the highest, called
      the {load water line}, indicates her proper submergence
      when loaded.

   {Water-line model} (Shipbuilding), a model of a vessel formed
      of boards which are shaped according to the water lines as
      shown in the plans and laid upon each other to form a
      solid model.