| secrecy(noun, issue, doubt, question, secret) |
| self-contradiction(noun, difficult, issue, question, task) |
| baffling mystery(expression, idiom, secret, mystery, brain-twister) |
| baffling problem(expression, idiom, secret, mystery, brain-twister) |
| confidential communication(expression, idiom, secret, mystery, brain-twister) |
| confoundment(noun, difficult, issue, question, task) |
| dark horse(expression, idiom, secret, mystery, brain-twister) |
| enigmatic question(expression, idiom, secret, mystery, brain-twister) |
| guarded secret(expression, idiom, secret, mystery, brain-twister) |
| mystique(noun, difficult, issue, question, task) |
| perplexed question(expression, idiom, secret, mystery, brain-twister) |
| private matter(expression, idiom, secret, mystery, brain-twister) |
| privileged communication(expression, idiom, secret, mystery, brain-twister) |
| profound secret(expression, idiom, secret, mystery, brain-twister) |
| puzzling thing(expression, idiom, secret, mystery, brain-twister) |
| restricted information(expression, idiom, secret, mystery, brain-twister) |
| unexplored ground(expression, idiom, secret, mystery, brain-twister) |
| unexplored territory(expression, idiom, secret, mystery, brain-twister) |
| charades(noun, secret, puzzle, mystery, riddle) |
| confidential information(expression, confidence, secret, puzzle, mystery) |