" aghast "

[Adjective]  | "aghast" | \ ə-ˈgast \

1: struck with terror, amazement, or horror : shocked and upset

Origin: 13th century ;

 Alteration (with after {see: |ghastly|ghastly}, {see: |ghost:1|ghost:1}) of Middle English agast, from past participle of agasten "to frighten, become frightened," from a-, perfective prefix + -gasten "to frighten," {mat|abide|}, {mat|gast|};

  * Note : Oxford English Dictionry, third edition, see:s agasten as formed with Middle English gasten, though this verb is not attested until more than a century later, suggesting that gasten may have been formed by dropping the prefix from agasten. Old English gǣstan is attested only once, in Cynewulf's Juliana, and the sense appears to be closer to "afflict" than "frighten." The prefix a- in the modern adjective aghast has presumably been construed as {a-:1|a-:1}.;

[Adjective]  | "aghast"