[ non-pluhst ]
/ nɒnˈplʌst /
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completely puzzled or perplexed by something unexpected: She blows a hole in the wall and escapes, and the nonplussed aliens are left wondering what happened.
Nonstandard. not dismayed; indifferent or unexcited; calm: I hadn’t yet told my girlfriend I was leaving—I didn't want to risk being crushed by a nonplussed response to the news.
the simple past tense and past participle of nonplus.
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Question 1 of 6
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Sometimes non·plused .

Origin of nonplussed

First recorded in 1600–10; nonplus + -ed2

usage note for nonplussed

In correct usage, nonplussed means “puzzled or perplexed”: Her odd choice of words left me somewhat nonplussed. However, there is a more recent, generally unfamiliar usage, meaning “not dismayed; indifferent or unexcited”: He imitated the nonplussed expression of the character Spock on Star Trek. This newer meaning can be ambiguous, since it is almost the opposite of the original meaning. Partly for this reason, it is not accepted as standard usage and should generally be avoided.
One explanation for the nonstandard meaning is the analysis of nonplussed as non- “not” + plussed, misinterpreted as “not puzzled or perplexed,” possibly on analogy with other words having a negative prefix and similar meaning, such as nonchalant. However, plussed has no real meaning in English. Rather, the adjective nonplussed was formed from the less common verb nonplus “to puzzle or perplex,” originally a noun meaning “a state of utter perplexity,” borrowed from the Latin phrase nōn plūs “not more; no further.” A state of perplexity is one in which no more can be said or done.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use nonplussed in a sentence