| rebus(difficulty, question, secret, puzzle, subtlety) |
| recondite |
| riddle(difficulty, question, secret, puzzle, obscurity) |
| rigor |
| rigour |
| rune(difficulty, question, secret, puzzle, subtlety) |
| secrecy(difficulty, question, secret, puzzle, obscurity) |
| secret(question, puzzle, perplexity, obscurity, subtlety) |
| sphinx(difficulty, question, secret, puzzle, perplexity) |
| stickler(difficulty, question, secret, puzzle, obscurity) |
| stumper(difficulty, question, secret, puzzle, perplexity) |
| teaser(difficulty, question, secret, puzzle, perplexity) |
| thriller(difficulty, question, secret, puzzle, subtlety) |
| toughness |
| twister(difficulty, question, secret, puzzle, obscurity) |
| whodunit(difficulty, question, secret, puzzle, subtlety) |
| why(difficulty, question, secret, puzzle, obscurity) |
| acumen |
| ambiguous |
| anagram(uncertainty, vagueness, haziness) |