| inscrutableness(noun, question, secret, puzzle, subtlety) |
| knot(noun, puzzle, riddle, enigma) |
| mind-breaker(noun, question, puzzle, riddle) |
| mindboggler(noun, question, secret, puzzle, subtlety) |
| mystification(noun, question, secret, puzzle, obscurity) |
| nut |
| occult(noun, question, secret, puzzle, subtlety) |
| oracle(noun, question, secret, puzzle, subtlety) |
| pun(noun, question, puzzle, riddle) |
| query(noun, challenge, question, puzzle, example) |
| question(noun, difficulty, secret, puzzle, obscurity) |
| rune(noun, question, secret, puzzle, subtlety) |
| secrecy(noun, difficulty, question, secret, puzzle) |
| sphinx(noun, difficulty, question, secret, puzzle) |
| stickler(noun, difficulty, challenge, question, secret) |
| subtlety(noun, difficulty, question, secret, puzzle) |
| thriller(noun, question, secret, puzzle, subtlety) |
| toughie |
| twister(noun, difficulty, challenge, question, secret) |
| whodunit(noun, question, secret, puzzle, subtlety) |