Synonyms:
- 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