Source : Webster's Revised Unabridged Dictionary (1913)

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

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

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

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.]

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

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

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

   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.

            The house of peers was somewhat appalled at this
            alarum.                               --Clarendon.

   Syn: To dismay; terrify; daunt; frighten; affright; scare;
        depress. See {Dismay}.

Source : WordNet®

appall
     v 1: strike with disgust or revulsion; "The scandalous behavior
          of this married woman shocked her friends" [syn: {shock},
           {offend}, {scandalize}, {scandalise}, {appal}, {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}, {horrify}]