The Collaborative International Dictionary of English v.0.48:

Pile \Pile\, n. [AS. p[imac]l arrow, stake, L. pilum javelin;
   but cf. also L. pila pillar.]
   1. A large stake, or piece of timber, pointed and driven into
      the earth, as at the bottom of a river, or in a harbor
      where the ground is soft, for the support of a building, a
      pier, or other superstructure, or to form a cofferdam,
      etc.
      [1913 Webster]

   Note: Tubular iron piles are now much used.
         [1913 Webster]

   2. [Cf. F. pile.] (Her.) One of the ordinaries or
      subordinaries having the form of a wedge, usually placed
      palewise, with the broadest end uppermost.
      [1913 Webster]

   Pile bridge, a bridge of which the roadway is supported on
      piles.

   Pile cap, a beam resting upon and connecting the heads of
      piles.

   Pile driver, or Pile engine, an apparatus for driving
      down piles, consisting usually of a high frame, with
      suitable appliances for raising to a height (by animal or
      steam power, the explosion of gunpowder, etc.) a heavy
      mass of iron, which falls upon the pile.

   Pile dwelling. See Lake dwelling, under Lake.

   Pile plank (Hydraul. Eng.), a thick plank used as a pile in
      sheet piling. See Sheet piling, under Piling.

   Pneumatic pile. See under Pneumatic.

   Screw pile, one with a screw at the lower end, and sunk by
      rotation aided by pressure.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pile driver
    n 1: a machine that drives piling into the ground