The Collaborative International Dictionary of English v.0.48:

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.
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   2. Fig.: That which supports or upholds, as a board does a
      swimmer.
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            His charity is a better plank than the faith of an
            intolerant and bitter-minded bigot.   --Southey.
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   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]
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   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.
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