| doubt(noun, concern, difficulty, anxiety, issue) |
| perplexity(noun, trouble, worry, concern, strain) |
| pickle(noun, fix, worry, difficulty, distress) |
| case(noun, point, difficulty, line, issue) |
| hitch(noun, trouble, difficulty, weakness, informal) |
| subject(noun, study, trouble, worry, concern) |
| bother(noun, trouble, defeat, worry, concern) |
| brain-teaser(noun, trouble, challenge, puzzle) |
| challenge(noun, verb, difficulty, issue, question) |
| nuisance(noun, trouble, person, bother, worry) |
| point(noun, concern, difficulty, line, interest) |
| stumper(noun, trouble, difficulty, challenge, question) |
| worry(noun, trouble, defeat, concern, strain) |
| can of worms(noun, expression, idiom, trouble, easy) |
| labyrinth(noun, secret, complexity, maze) |
| brainteaser(noun, difficulty, challenge, question, secret) |
| business(noun, trouble, worry, concern, point) |
| closed book(noun, expression, trouble, challenge, question) |
| crux(noun, trouble, difficulty, burden, challenge) |
| hindrance(noun, trouble, check, worry, delay) |