1. Filled with bewilderment
   "She was nonplussed by the unexpected turn of events";
   - at a loss, nonplused [US], puzzled, perplexed, thrown
    
2. [N. Amer, informal] Free from emotional agitation or nervous tension
   "the waiters were nonplussed and good natured";
   - unflurried, unflustered, unperturbed, unruffled, untroubled, unfazed [informal]

1. Confuse or leave at a loss because of something complex or difficult to understand
   "These questions nonplus even the experts";
   - confuse, throw, fox, befuddle, fuddle, bedevil, confound, discombobulate [informal], perplex, vex, stick, get, puzzle, mystify, baffle, beat, pose, bewilder, flummox, stupefy, gravel, dumbfound

See also: composed, figure out, perplexed, puzzle over

Type of: affect, bear on, bear upon, impact

Encyclopedia: Nonplus