Source : Webster's Revised Unabridged Dictionary (1913)

Nonplus \Non"plus`\, v. t. [imp. & p. p. {Nonplused}or
   {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.

Source : WordNet®

nonplussed
     adj : filled with bewilderment; "at a loss to understand those
           remarks"; "puzzled that she left without saying
           goodbye" [syn: {at a loss(p)}, {nonplused}, {puzzled}]

nonplus
     v : be a mystery or bewildering to; "This beats me!"; "Got me--I
         don't know the answer!"; "a vexing problem"; "This
         question really stuck me" [syn: {perplex}, {vex}, {stick},
          {get}, {puzzle}, {mystify}, {baffle}, {beat}, {pose}, {bewilder},
          {flummox}, {stupefy}, {gravel}, {amaze}, {dumbfound}]
     [also: {nonplussing}, {nonplusses}, {nonplussed}]

nonplussed
     See {nonplus}