| difficult question(noun, trouble, challenge, question, puzzle) |
| discord(noun, verb, difficult, issue, think) |
| inconsistency(noun, difficult, issue, question, absurdity) |
| jigsaw puzzle(expression, idiom, secret, mystery, brain-twister) |
| knot(noun, informal, question, secret, dilemma) |
| nonsense(noun, difficult, issue, question, absurdity) |
| open question(noun, expression, idiom, question, secret) |
| parable(noun, question, secret, dilemma, mystery) |
| plain question(noun, expression, idiom, question, secret) |
| point in dispute(noun, expression, idiom, question, secret) |
| question at issue(noun, expression, idiom, question, secret) |
| screen(noun, verb, difficult, issue, think) |
| sealed book(noun, expression, idiom, problem, secret) |
| sixty-four dollar question(noun, expression, idiom, question, secret) |
| subject of controversy(noun, expression, idiom, question, secret) |
| subject of inquiry(noun, expression, idiom, question, secret) |
| Gordian knot(noun, question, secret, dilemma, mystery) |
| baffle(noun, verb, difficult, issue, think) |
| bother(noun, verb, difficult, issue, think) |
| classified information(expression, idiom, confidence, secret, mystery) |