Synonyms and related words :
Chinese puzzle, Gordian knot, arcanum, baffle, bafflement, baffling problem, bewilderment, bother, brain twister, cabala, classified information, confidence, confidential communication, confoundment, confusion, conundrum, crossword puzzle, crux, dark horse, dilemma, discomposure, disconcert, disconcertedness, disconcertion, disconcertment, disturbance, embarrassment, enigmatic question, esoterica, fix, floorer, frontier, frontiers of knowledge, guarded secret, hermetics, jam, jigsaw puzzle, knot, knotty point, matter of ignorance, mind-boggler, mystery, mystery of mysteries, mystification, n, node, nodus, nonplus, nut to crack, oxymoron, paradox, perplexed question, perplexity, personal matter, perturbation, pickle, plight, pons asinorum, poser, pother, predicament, private matter, privileged communication, privity, problem, profound secret, puzzle, puzzlement, puzzler, quandary, question, question mark, restricted information, riddle, scrape, sealed book, secret, sixty-four dollar question, stew, sticker, stumper, teaser, terra incognita, the incalculable, the occult, the strange, the unfamiliar, the unknowable, the unknown, tough proposition, unassuredness, unexplored ground, unexplored territory, unknown quantity, upset, vexed question, why, x, z