usage note for nonplussed
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.
How to use nonplussed in a sentence
The prisoner was evidently nonplused, but it was only for a moment.Scotch Wit and Humor|W. H. (Walter Henry) Howe
“I will,” promised Tom, somewhat nonplused at the outcome of the affair.The Winning Touchdown|Lester Chadwick
And for a moment she stared at the scene, nonplused, discomfited.The White Moll|Frank L. Packard
Something had gone wrong in the engine room, and the engineer was nonplused."Say Fellows--"|Wade C. Smith
Mr. Reginald Kent looked rather nonplused and Mr. Tucker handed me his gun to hold while he rolled in the leaves for very joy.At Boarding School with the Tucker Twins|Nell Speed