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
inquiry, request, search, research, quest, pursuit, examination, review, scrutiny, investigation, indagation, perquisition, perscrutation, pervestigation, inquest, inquisition, exploration, exploitation, ventilation, sifting, calculation, analysis, dissection, resolution, induction, Baconian method, strict inquiry, close inquiry, searching inquiry, exhaustive inquiry, narrow search, strict search, study, scire facias, ad referendum, trial, questioning, interrogation, interrogatory, interpellation, challenge, examination, cross-examination, catechism, feeler, Socratic method, zetetic philosophy, leading question, discussion, reconnoitering, reconnaissance, prying, espionage, espionnage, domiciliary visit, peep behind the curtain, lantern of Diogenes, question, query, problem, desideratum, point to be solved, porism, subject of inquiry, field of inquiry, subject of controversy, point in dispute, matter in dispute, moot point, issue, question at issue, bone of contention, plain question, fair question, open question, enigma
, knotty point, quodlibet, threshold of an inquiry, inquirer, investigator, inquisitor, inspector, querist, examiner, catechist, scrutator scrutineer scrutinizer, analyst, quidnunc, inquiry, inquisitive, requisitive, requisitory, catechetical, inquisitorial, analytic, in search of, in quest of, on the lookout for, interrogative, zetetic, all searching, undetermined, untried, undecided, in question, in dispute, in issue, in course of inquiry, under discussion, under consideration, under investigation, sub judice, moot, proposed, doubtful, quaere?, what?, why?, wherefore?, whence?, whither?, where?, how comes it?, how happens it?, how is it?, what is the reason?, what's the matter?, nicht wahr?, what's in the wind?, what on earth?, when?, who?.
unintelligibility, incomprehensibility, imperspicuity, inconceivableness, vagueness, obscurity, ambiguity, doubtful meaning, uncertainty, perplexity, spinosity, obscurum per obscurius, mystification, latency, transcendentalism, paradox, oxymoron, riddle, enigma
, puzzle, diagnus vindice nodus, sealed book, steganography, freemasonry, pons asinorum, asses' bridge, high Dutch, Greek, Hebrew, jargon, unintelligible, unaccountable, undecipherable, undiscoverable, unknowable, unfathomable, incognizable, inexplicable, inscrutable, inapprehensible, incomprehensible, insolvable, insoluble, impenetrable, illegible, as Greek to one, unexplained, paradoxical, enigmatic, enigmatical, puzzling (secret), indecipherable, obscure, dark, muddy, clear as mud, seen through a mist, dim, nebulous, shrouded in mystery, opaque, dense, undiscernible, misty, hidden, latent, indefinite, garbled, perplexed, undetermined, vague, loose, ambiguous, mysterious, mystic, mystical, acroamatic, acroamatical, metempirical, transcendental, occult, recondite, abstruse, crabbed, inconceivable, inconceptible, searchless, above comprehension, beyond comprehension, past comprehension, beyond one's depth, unconceived, inexpressible, undefinable, incommunicable, unpredictable, unforeseeable, it's Greek to me.
secret, dead secret, profound secret, arcanum, mystery, latency, Asian mystery, sealed book, secrets of the prison house, le desous des cartes, enigma
, riddle, puzzle, nut to crack, conundrum, charade, rebus, logogriph, monogram, anagram, Sphinx, crux criticorum, maze, labyrinth, Hyrcynian wood, intricacy, meander, problem, paradox, unintelligibility, terra incognita, secret, involved, labyrinthine, labyrinthian, mazy, confidential, top secret.