nonplus

This verb describes a specific state of mental paralysis where a person is so bewildered or taken aback that they are momentarily unable to respond. It carries a stronger connotation of helplessness than "confuse" or "surprise," suggesting a total loss for words or a temporary cognitive freeze.

In modern usage, the word is more frequently encountered as the past participle adjective "nonplussed." While the verb form is correct, it is often perceived as formal or literary. Users should be aware of a regional variation in North American English where "nonplussed" is occasionally misused to mean "unperturbed" or "unfazed," which is the exact opposite of its standard dictionary definition.