The Collaborative International Dictionary of English v.0.48:

Appall \Ap*pall"\, n.
   Terror; dismay. [Poet.] --Cowper.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Appall \Ap*pall"\, v. t. [imp. & p. p. Appalled; p. pr. & vb.
   n. Appalling.] [OF. appalir to grow pale, make pale; a (L.
   ad) + p[^a]lir to grow pale, to make pale, p[^a]le pale. See
   Pale, a., and cf. Pall.]
   1. To make pale; to blanch. [Obs.]
      [1913 Webster]

            The answer that ye made to me, my dear, . . .
            Hath so appalled my countenance.      --Wyatt.
      [1913 Webster]

   2. To weaken; to enfeeble; to reduce; as, an old appalled
      wight. [Obs.] --Chaucer.
      [1913 Webster]

            Wine, of its own nature, will not congeal and
            freeze, only it will lose the strength, and become
            appalled in extremity of cold.        --Holland.
      [1913 Webster]

   3. To depress or discourage with fear; to impress with fear
      in such a manner that the mind shrinks, or loses its
      firmness; to overcome with sudden terror or horror; to
      dismay; as, the sight appalled the stoutest heart.
      [1913 Webster]

            The house of peers was somewhat appalled at this
            alarum.                               --Clarendon.
      [1913 Webster]

   Syn: To dismay; terrify; daunt; frighten; affright; scare;
        depress. See Dismay.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Appall \Ap*pall"\, v. i.
   1. To grow faint; to become weak; to become dismayed or
      discouraged. [Obs.] --Gower.
      [1913 Webster]

   2. To lose flavor or become stale. [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

appall
    v 1: strike with disgust or revulsion; "The scandalous behavior
         of this married woman shocked her friends" [syn: shock,
         offend, scandalize, scandalise, appal, appall,
         outrage]
    2: fill with apprehension or alarm; cause to be unpleasantly
       surprised; "I was horrified at the thought of being late for
       my interview"; "The news of the executions horrified us"
       [syn: dismay, alarm, appal, appall, horrify]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "appall":
   abash, astound, awe, confound, daunt, discomfit, disconcert,
   disgust, dismay, faze, freeze, give offense, gross out, horrify,
   nauseate, offend, overawe, paralyze, petrify, put off, put out,
   repel, revolt, scare stiff, scare to death, shake, shock, sicken,
   strike dumb, strike terror into, stun, stupefy, take aback,
   terrify, turn the stomach