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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The Collaborative International Dictionary of English v.0.48:

Plank \Plank\, v. t. [imp. & p. p. Planked; p. pr. & vb. n.
   Planking.]
   1. To cover or lay with planks; as, to plank a floor or a
      ship. "Planked with pine." --Dryden.
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   2. To lay down, as on a plank or table; to stake or pay cash;
      as, to plank money in a wager. [Colloq. U.S.]
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   3. To harden, as hat bodies, by felting.
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   4. (Wooden Manuf.) To splice together the ends of slivers of
      wool, for subsequent drawing.
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   Planked shad, shad split open, fastened to a plank, and
      roasted before a wood fire.
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WordNet (r) 3.0 (2006):

plank
    n 1: a stout length of sawn timber; made in a wide variety of
         sizes and used for many purposes [syn: board, plank]
    2: an endorsed policy in the platform of a political party
    v 1: cover with planks; "The streets were planked" [syn:
         plank, plank over]
    2: set (something or oneself) down with or as if with a noise;
       "He planked the money on the table"; "He planked himself into
       the sofa" [syn: plank, flump, plonk, plop, plunk,
       plump down, plunk down, plump]
    3: cook and serve on a plank; "Planked vegetable"; "Planked
       shad"