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