flabbergasted
1. [ adjective ] as if struck dumb with astonishment and surprise
Synonyms: dumfounded thunderstruck stupefied dumbfounded
Examples:

"a circle of policemen stood dumbfounded by her denial of having seem the accident" "the flabbergasted aldermen were speechless" "was thunderstruck by the news of his promotion"

Related terms: surprised
Similar spelling:   flabbergast