nonplussed• "I don't know, " he said, nonplussed at the question.
nonplussed by/at• Joan's great skill, then as now, was to be completely nonplussed by anything Richard did.• George knew that she was a bitnonplussed at his eagerness for her to have her own social life.• Even Orozco seems nonplussed by his fame.• Mundin is nonplussed at our lack of proper titillation.• Factory were a little nonplussed by the decision.• And, faced with this question, most men are totally nonplussed at the idea.
Originnonplussed
(1500-1600)nonplus“state of confusion”((16-19 centuries)), from Latinnon plus“no more”