A-ghäst', a. or adv.

a. or adv. [A contraction of agazed (q. v.), the p. p. of agaze; O. Eng. also agasted.] Struck with amazement; stupefied with sudden fright or horror.

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

☞ Spenser uses the word as the past tense of the verb agaze:

That seemed from some feared foe to fly, Or other grisly thing that him aghast. Faery Qu. I. 184.