The Collaborative International Dictionary of English v.0.48:

Aghast \A*ghast"\, v. t.
   See Agast, v. t. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Aghast \A*ghast"\, a. & p. p. [OE. agast, agasted, p. p. of
   agasten to terrify, fr. AS. pref. [=a]- (cf. Goth. us-, G.
   er-, orig. meaning out) + g?stan to terrify, torment: cf.
   Goth. usgaisjan to terrify, primitively to fix, to root to
   the spot with terror; akin to L. haerere to stick fast,
   cling. See Gaze, Hesitate.]
   Terrified; struck with amazement; showing signs of terror or
   horror.
   [1913 Webster]

         Aghast he waked; and, starting from his bed,
         Cold sweat in clammy drops his limbs o'erspread.
                                                  --Dryden.
   [1913 Webster]

         The commissioners read and stood aghast. --Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Agast \A*gast"\ or Aghast \A*ghast"\, v. t.
   To affright; to terrify. [Obs.] --Chaucer. Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

aghast
    adj 1: struck with fear, dread, or consternation [syn:
           aghast(p), appalled, dismayed, shocked]