The Collaborative International Dictionary of English v.0.48:

Impale \Im*pale"\, v. t. [imp. & p. p. Impaled; p. pr. & vb.
   n. Impaling.] [See 2d Empale.]
   1. To pierce with a pale; to put to death by fixing on a
      sharp stake. See Empale.
      [1913 Webster]

            Then with what life remains, impaled, and left
            To writhe at leisure round the bloody stake.
                                                  --Addison.
      [1913 Webster]

   2. To inclose, as with pales or stakes; to surround.
      [1913 Webster]

            Impale him with your weapons round about. --Shak.
      [1913 Webster]

            Impenetrable, impaled with circling fire. --Milton.
      [1913 Webster]

   3. (Her.) To join, as two coats of arms on one shield,
      palewise; hence, to join in honorable mention.
      [1913 Webster]

            Ordered the admission of St. Patrick to the same to
            be matched and impaled with the blessed Virgin in
            the honor thereof.                    --Fuller.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Empale \Em*pale"\, v. t. [imp. & p. p. Empaled; p. pr. & vb.
   n. Empaling.] [OF. empaler to palisade, pierce, F. empaler
   to punish by empalement; pref. em- (L. in) + OF. & F. pal a
   pale, stake. See Pale a stake, and cf. Impale.] [Written
   also impale.]
   1. To fence or fortify with stakes; to surround with a line
      of stakes for defense; to impale.
      [1913 Webster]

            All that dwell near enemies empale villages, to save
            themselves from surprise.             --Sir W.
                                                  Raleigh.
      [1913 Webster]

   2. To inclose; to surround. See Impale.
      [1913 Webster]

   3. To put to death by thrusting a sharpened stake through the
      body.
      [1913 Webster]

   4. (Her.) Same as Impale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impale
    v 1: pierce with a sharp stake or point; "impale a shrimp on a
         skewer" [syn: transfix, impale, empale, spike]
    2: kill by piercing with a spear or sharp pole; "the enemies
       were impaled and left to die" [syn: impale, stake]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "impale":
   agonize, auger, bayonet, bite, bloody, bore, broach, claw,
   convulse, countersink, crucify, dagger, dirk, dismember,
   draw and quarter, drill, empierce, excruciate, fix, gore, gouge,
   gouge out, grill, harrow, hole, honeycomb, keelhaul,
   kill by inches, knife, lacerate, lance, lancinate, macerate,
   martyr, martyrize, needle, penetrate, perforate, picket, pierce,
   pink, plunge in, poniard, prick, punch, puncture, punish, rack,
   ream, ream out, riddle, rip, run through, saber, savage, scarify,
   skewer, spear, spike, spit, stab, stick, stiletto, sword, tap,
   tar and feather, torment, torture, transfix, transpierce, trepan,
   trephine, wring



The Devil's Dictionary (1881-1906):

IMPALE, v.t.  In popular usage to pierce with any weapon which remains
fixed in the wound.  This, however, is inaccurate; to impale is,
properly, to put to death by thrusting an upright sharp stake into the
body, the victim being left in a sitting position.  This was a common
mode of punishment among many of the nations of antiquity, and is
still in high favor in China and other parts of Asia.  Down to the
beginning of the fifteenth century it was widely employed in
"churching" heretics and schismatics.  Wolecraft calls it the "stoole
of repentynge," and among the common people it was jocularly known as
"riding the one legged horse."  Ludwig Salzmann informs us that in
Thibet impalement is considered the most appropriate punishment for
crimes against religion; and although in China it is sometimes awarded
for secular offences, it is most frequently adjudged in cases of
sacrilege.  To the person in actual experience of impalement it must
be a matter of minor importance by what kind of civil or religious
dissent he was made acquainted with its discomforts; but doubtless he
would feel a certain satisfaction if able to contemplate himself in
the character of a weather-cock on the spire of the True Church.