The Collaborative International Dictionary of English v.0.48:

Impalement \Im*pale"ment\, n.
   1. The act of impaling, or the state of being impaled.
      --Byron.
      [1913 Webster]

   2. An inclosing by stakes or pales, or the space so inclosed.
      --H. Brooke.
      [1913 Webster]

   3. That which hedges in; inclosure. [R.] --Milton.
      [1913 Webster]

   4. (Her.) The division of a shield palewise, or by a vertical
      line, esp. for the purpose of putting side by side the
      arms of husband and wife. See Impale, 3.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Empalement \Em*pale"ment\, n. [Cf. F. empalement, fr. empaler.
   See Empale.] [Written also impalement.]
   1. A fencing, inclosing, or fortifying with stakes.
      [1913 Webster]

   2. A putting to death by thrusting a sharpened stake through
      the body.
      [1913 Webster]

   3. (Her.) Same as Impalement.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impalement
    n 1: the act of piercing with a sharpened stake as a form of
         punishment or torture