From today’s Webster’s Word of the Day:

nonplusnahn-PLUS
DEFINITION
verb
: to cause to be at a loss as to what to say, think, or do : perplex
EXAMPLES
“I spent a few days making phone calls, talking to perplexed and befuddled healthcare providers who were absolutely nonplussed by the fact that I wanted to pay them rapidly depreciating American dollars to provide me with healthcare services.” — From Kevin Williamson’s 2011 book The Politically Incorrect Guide to Socialism