From The Collaborative International Dictionary of English v.0.48 [gcide]:
Nonplus \Non"plus\, n. [L. non not + plus more, further. See
Plural.]
A state or condition which baffles reason or confounds
judgment; insuperable difficulty; inability to proceed or
decide; puzzle; quandary.
[1913 Webster]
Both of them are a perfect nonplus and baffle to all
human understanding. --South.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
[1913 Webster]
He has been nonplused by Mr. Dry's desiring him to tell
what it was that he endeavored to prove. --Spectator.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
nonplus
v 1: 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, nonplus, gravel,
amaze, dumbfound]