FLUMMOX
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
Of uncertain origin, probably risen out of a British dialect (OED finds candidate words in Herefordshire, Gloucestershire, southern Cheshire, and Sheffield). "The formation seems to be onomatopœic, expressive of the notion of throwing down roughly and untidily" [OED].
Verb
flummox (third-person singular simple present flummoxes, present participle flummoxing, simple past and past participle flummoxed)
To confuse; to fluster; to flabbergast.
Synonyms
• See also confuse
Source: Wiktionary