nonplussed adjective
also US nonplused /ˌnɑːnˈplʌst/ also US nonplused /ˌnɑːnˈplʌst/ Learner's definition of NONPLUSSED
not used before a noun [more nonplussed; most nonplussed] formal
: so surprised or confused by something that you do not know what to say, think, or do : perplexed惊呆;不知所措