nonplus

From Latin nōn plūs (“no more, no further”)

nonplus (plural nonpluses)

1. A state of perplexity or bewilderment.
   • 1603, John Florio, transl.; Michel de Montaigne, chapter 46, in The Essayes, […], book I, printed at London: By Val[entine] Simmes for Edward Blount […], OCLC 946730821:

     altering Vaudemont, to Vallemontanus, and metamorphosing them, by suting them to the Græcian or Latin tongue, we know not what to make of them, and are often at a non-plus.

   • South

     Both of them are a perfect nonplus and baffle to all human understanding.

nonplus (third-person singular simple present nonplusses or nonpluses, present participle nonplussing or nonplusing, simple past and past participle nonplussed or nonplused)

1. (transitive) to perplex or bewilder someone; to confound or flummox

• nonplussed