Synonyms for Flabbergasted (same or very similar meaning)
WordNet sense 1 (as if struck dumb with astonishment and surprise):
dumbfounded, dumbstruck, stupefied, thunderstruck, dumfounded, dumbstricken
WordNet sense 2 (taken unawares or suddenly and feeling wonder or astonishment):
surprised
From the ODE community, based on WordNet
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