Often used when something is so surprising it causes confusion and stops you from reacting quickly. After the magician vanished, the audience was completely nonplussed.
Pro Tip 2/3
Unexpected Situations
Use 'nonplussed' to describe someone's reaction to events they didn't foresee and don't know how to handle. When the lights went out during her presentation, she stood nonplussed.
Pro Tip 3/3
Subtle Reaction
The reaction is internal, so someone might appear calm but is actually nonplussed. Despite her composed face, she felt completely nonplussed.