| No. | Item | Definition |
|---|---|---|
| 1. | ambiguity | unclear meaning or uncertainty |
| 2. | anomaly | something hard to account for |
| 3. | awkward problem | a difficult delicate problem |
| 4. | baffling thing | something very confusing |
| 5. | bemuse | to confuse or puzzle mildly |
| 6. | bewilderer | something that bewilders |
| 7. | bewildering thing | something hard to understand |
| 8. | bewilderment | a feeling of confusion |
| 9. | bind | a difficult situation or dilemma |
| 10. | bother | a source of difficulty |
| 11. | brain-teaser | a problem meant to challenge thinking |
| 12. | case | a particular problem or matter |
| 13. | catch | a hidden difficulty or drawback |
| 14. | challenge | a demanding task or issue |
| 15. | complex problem | a problem with many parts |
| 16. | complication | something that makes matters harder |
| 17. | confounder | something that confuses greatly |
| 18. | conundrum | a confusing and difficult problem |
| 19. | corker | something remarkably difficult or striking |
| 20. | cracker | something exceptionally difficult |
| 21. | crossword | a word-based thinking challenge |
| 22. | delicate issue | a sensitive difficult matter |
| 23. | difficult matter | a hard issue to resolve |
| 24. | difficulty | something hard to deal with |
| 25. | dilemma | a difficult choice or situation |
| 26. | doozy | something notably difficult or odd |
| 27. | enigma | a baffling or mysterious thing |
| 28. | entangle | to involve in complications |
| 29. | fix | a troublesome situation |
| 30. | glitch | a small unexpected problem |
| 31. | hard case | a difficult matter |
| 32. | hard nut | a difficult problem to crack |
| 33. | hard question | a difficult question |
| 34. | head-scratcher | something confusing or perplexing |
| 35. | headache | a troublesome problem |
| 36. | hitch | a small problem or snag |
| 37. | issue | an important problem or matter |
| 38. | jam | a difficult situation |
| 39. | jigsaw | a piece-assembly thinking challenge |
| 40. | kicker | an unexpected difficult point |
| 41. | knot | a difficult or tangled issue |
| 42. | knotty problem | a very difficult problem |
| 43. | labyrinth | a very confusing situation |
| 44. | logic problem | a problem requiring reasoning |
| 45. | maze | a confusing network or situation |
| 46. | mental challenge | something testing the mind |
| 47. | mess | a confused or difficult situation |
| 48. | mind-bender | something extremely hard to grasp |
| 49. | mindboggler | something astonishingly confusing |
| 50. | muddle | a confused situation |
| 51. | mysterious thing | something unexplained or obscure |
| 52. | mystery | something hard to understand or explain |
| 53. | mystification | something that causes confusion |
| 54. | mystifier | something that confuses people |
| 55. | nasty one | a difficult unpleasant problem |
| 56. | nightmare | a very difficult problem |
| 57. | nut | a difficult problem |
| 58. | obscure | to make hard to understand |
| 59. | obscurity | something hard to understand |
| 60. | obstacle | something that blocks progress |
| 61. | oddity | something strange or hard to explain |
| 62. | paradox | a seemingly contradictory problem |
| 63. | perplexer | something that perplexes |
| 64. | perplexing thing | something confusing and difficult |
| 65. | pickle | a difficult or awkward situation |
| 66. | point | a specific issue or difficulty |
| 67. | poser | a difficult question or problem |
| 68. | predicament | a difficult unpleasant situation |
| 69. | problem | a matter needing a solution |
| 70. | puzzler | something difficult to understand |
| 71. | quandary | a state of uncertainty |
| 72. | question | a matter needing thought |
| 73. | rack | to strain mentally |
| 74. | rebus | a picture-and-word riddle |
| 75. | riddle | a puzzling question or problem |
| 76. | rough one | a difficult problem or situation |
| 77. | rub | the difficult part of something |
| 78. | snag | an unexpected problem or obstacle |
| 79. | spot | a difficult situation |
| 80. | sticking point | the main difficulty in something |
| 81. | sticky problem | a hard awkward problem |
| 82. | stumbling block | something that hinders progress |
| 83. | stump | to leave unable to answer |
| 84. | stumper | something very hard to solve |
| 85. | sudoku | a number-placement thinking challenge |
| 86. | tangle | a complicated confused situation |
| 87. | teaser | something that tests ingenuity |
| 88. | teasing question | a mentally challenging question |
| 89. | thorny issue | a difficult complicated matter |
| 90. | ticklish problem | a delicate difficult problem |
| 91. | tight spot | a difficult situation |
| 92. | tough case | a difficult matter or problem |
| 93. | tough nut | a difficult problem or person |
| 94. | tough question | a difficult question |
| 95. | tricky question | a confusing question |
| 96. | unknown | something not yet understood |
| 97. | vex | to trouble or perplex |
| 98. | vexed question | a difficult debated problem |
| 99. | vexing problem | an annoying difficult problem |
| 100. | word problem | a problem stated in words |