"dumbfounded" in the verb sense
1. perplex, vex, stick, get, puzzle, mystify, baffle, beat, pose, bewilder, flummox, stupefy, nonplus, gravel, amaze, dumbfound
be a mystery or bewildering to
"This beats me!"
"Got me
"dumbfounded" in the adjective sense
1. dumbfounded, dumfounded, flabbergasted, stupefied, thunderstruck, dumbstruck, dumbstricken
as if struck dumb with astonishment and surprise
"a circle of policemen stood dumbfounded by her denial of having seen the accident"
"the flabbergasted aldermen were speechless"
"was thunderstruck by the news of his promotion"
Source: WordNet® (An amazing lexical database of English)
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