/euh gast", euh gahst"/ , adj.
struck with overwhelming shock or amazement; filled with sudden fright or horror: They stood aghast at the sight of the plane crashing.
[ 1225-75; ME agast frightened, ptp. of agasten, equiv. to a- A- 3 + gasten, OE gaestan to frighten, earlier * gastjan gaistjan; see GHOST ]