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]

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "aghast":
   afraid, agape, agog, all agog, amazed, anxious, appalled, ashen,
   astonished, astounded, at gaze, awed, awestricken, awestruck,
   beguiled, bewildered, bewitched, blanched, breathless, captivated,
   confounded, cowed, deadly pale, dismayed, dumbfounded, dumbstruck,
   enchanted, enraptured, enravished, enthralled, entranced,
   fascinated, fearful, flabbergasted, frightened, frozen, gaping,
   gauping, gazing, gray with fear, horrified, horror-struck,
   hypnotized, in awe, in awe of, intimidated, lost in wonder,
   marveling, mesmerized, open-eyed, openmouthed, overwhelmed,
   pale as death, pallid, paralyzed, petrified, popeyed, puzzled,
   rapt in wonder, scared, scared stiff, scared to death, scary,
   shocked, spellbound, staggered, staring, startled, stunned,
   stupefied, surprised, taken aback, terrified, terror-crazed,
   terror-haunted, terror-ridden, terror-riven, terror-shaken,
   terror-smitten, terror-struck, terror-troubled, thunderstruck,
   under a charm, undone, unmanned, unnerved, unstrung, wide-eyed,
   wonder-struck, wondering