From WordNet (r) 3.0 (2006) [wn]:
flabbergasted
adj 1: as if struck dumb with astonishment and surprise; "a
circle of policement stood dumbfounded by her denial of
having seen the accident"; "the flabbergasted aldermen
were speechless"; "was thunderstruck by the news of his
promotion" [syn: dumbfounded, dumfounded,
flabbergasted, stupefied, thunderstruck,
dumbstruck, dumbstricken]