nonplussed
adjective
UK/ˌnɒnˈplʌst/
US/ˌnɑːnˈplʌst/
Definitions of nonplussed adjective
Feeling surprised, confused, and uncertain about how to respond.
She was completely nonplussed upon hearing the news.
He seemed somewhat nonplussed when faced with such a complex problem.
The sudden request left them all a bit nonplussed.