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}]
Source: WordNet® 2.0