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.
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
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
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.