Nonplus

Part of speech: verb, noun

Definitions

1. To puzzle or bewilder someone so thoroughly that they do not know how to respond or what to do next
2. Describing a situation that leaves a person utterly baffled, unable to think of any way forward or reply
3. Completely confounding a person, or the state of being left at a total loss and unable to react

Etymology: The Latin phrase "nōn plūs" meant "no further" or "no more," and English took it up as a noun for a state of helpless perplexity: a point where no move seems possible. The noun comes from that phrase, with "nōn" meaning "not" and "plūs" meaning "more, further," and the Latin phrase itself traces back to the ancient root *pleh₁-, "to fill." The verb was later formed from the noun, so to nonplus someone is to leave them stuck, with no answer and no next step.

Synonyms: baffle, perplex, bewilder, confound, stump