Source : Webster's Revised Unabridged Dictionary (1913)

Plank \Plank\, n. [OE. planke, OF. planque, planche, F. planche,
   fr. L. planca; cf. Gr. ?, ?, anything flat and broad. Cf.
   {Planch}.]
   1. A broad piece of sawed timber, differing from a board only
      in being thicker. See {Board}.

   2. Fig.: That which supports or upholds, as a board does a
      swimmer.

            His charity is a better plank than the faith of an
            intolerant and bitter-minded bigot.   --Southey.

   3. One of the separate articles in a declaration of the
      principles of a party or cause; as, a plank in the
      national platform. [Cant]

   {Plank road}, or {Plank way}, a road surface formed of
      planks. [U.S.]

   {To walk the plank}, to walk along a plank laid across the
      bulwark of a ship, until one overbalances it and falls
      into the sea; -- a method of disposing of captives
      practiced by pirates.