| charade(noun, question, secret, puzzle, brain-twister) |
| crux criticorum(noun, expression, idiom, secret, brain) |
| field of inquiry(noun, expression, idiom, question, secret) |
| knotty point(noun, expression, idiom, question, secret) |
| matter in dispute(noun, expression, idiom, question, secret) |
| moot point(noun, expression, idiom, question, secret) |
| quiz(noun, verb, difficult, issue, think) |
| rebus(noun, question, secret, puzzle, brain-twister) |
| nonplus(noun, verb, difficult, issue, think) |
| quandary(noun, trouble, difficult, issue, challenge) |
| brain twister(noun, expression, idiom, difficult, issue) |
| mind-boggler(noun, challenge, question, problem, secret) |
| obscurity(noun, difficult, issue, question, secret) |
| trouble(noun, verb, adjective, difficult, issue) |
| vexed question(noun, expression, idiom, trouble, challenge) |
| ambiguity(noun, uncertainty, absurdity, obscurity, vagueness) |
| challenge(noun, verb, difficulty, difficult, issue) |
| cliffhanger(noun, difficulty, question, secret, puzzle) |
| desideratum(noun, difficult, issue, question, task) |
| diagnus vindice nodus(noun, expression, idiom, problem, secret) |