WordNet (r) 3.0 (2006):

dumbstricken
    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]