nonplussed

动词 nonplus:

1. be a mystery or bewildering to
   同义词：perplex, vex, stick, get, puzzle, mystify, baffle, beat, pose, bewilder, flummox, stupefy, nonplus, gravel, amaze, dumbfound

形容词 nonplussed:

1. filled with bewilderment
   同义词：at a loss, nonplused, puzzled

1. The professor is never at a nonplus, and never perplexed by a problem.
   那位教授从来不会感到困惑，也不会被任何问题所难倒。
2. I was completely nonplussed by his sudden appearance.
   他突然出现使我大吃一惊。