tr.v. non·plussed, non·plus·sing, non·plus·ses also non·plused or non·plus·ing or non·plus·es
1. To put at a loss as to what to think, say, or do; bewilder.
2. Usage Problem To cause to feel indifferent or bored.
A state of bewilderment or perplexity.
[From Latin nōn plūs, no more : nōn, not; see NON- + plūs, more; see pelə-1 in the Appendix of Indo-European roots.]
Usage Note: The verb nonplus, from the Latin phrase nōn plūs, "not more," is well established with the meaning "to surprise and bewilder." The verb and its participial adjective nonplussed often imply that the affected person is at a loss for words. This use of the word was acceptable to 90 percent of the Usage Panel in our 2013 survey in the sentence The scientists were completely nonplussed—the apparatus had not acted at all as they had expected. However, the word is frequently used to mean "to make indifferent, bore," as if the plus part of the word meant "to overcome with excitement." This usage is still controversial and should probably be avoided, since it may well be viewed as a mistake. In our 2013 survey, 57 percent of the Panel rejected the sentence The nine panelists showed little emotion during the broadcast and were generally nonplussed by the outcome. This percentage is almost unchanged from the 61 percent of the Panel who rejected the same sentence in 2001.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.