The Collaborative International Dictionary
Nonplusing
Nonplus \Non"plus`\, v. t. [imp. & p. p. Nonplusedor Nonplussed; p. pr. & vb. n. Nonplusing or Nonplussing.] To puzzle; to confound; to perplex; to cause to stop by embarrassment.
He has been nonplused by Mr. Dry's desiring him to tell
what it was that he endeavored to prove.
--Spectator.
Wiktionary
nonplusing
vb. (present participle of nonplus English)