NONPLUS
perplex, vex, stick, get, puzzle, mystify, baffle, beat, pose, bewilder, flummox, stupefy, nonplus, gravel, amaze, dumbfound
(verb) 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”
Source: WordNet® 3.1
Etymology
Noun
nonplus (plural nonpluses)
A state of perplexity or bewilderment.
Verb
nonplus (third-person singular simple present nonpluses or nonplusses, present participle nonplusing or nonplussing, simple past and past participle nonplused or nonplussed)
(transitive) to perplex or bewilder someone; to confound or flummox
Source: Wiktionary
Non"plus, n. Etym: [L. non not + plus more, further. See Plural.]
Definition: A state or condition which daffles reason or confounds
judgment; insuperable difficalty; inability to proceed or decide;
puzzle; quandary.
Both of them are a perfect nonplus and baffle to all human
understanding. South.
Non"plus`, v. t. [imp. & p. p. Nonplused or Nonplussed; p. pr. & vb.
n. Nonplusing or Nonplussing.]
Definition: 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: Webster’s Unabridged Dictionary 1913 Edition