| Knot |
| Poser? |
| Riddle |
| Puzzle |
| Sphinx |
| Problem |
| Toughie |
| Puzzler |
| Stumper |
| Baffler |
| Mystery |
| Perplexer |
| Conundrum |
| Real poser |
| Puzzlement |
| Perplexity |
| Brainteaser |
| Hard puzzle |
| ___ paradox |
| Real puzzle |
| WWII cipher |
| Closed book |
| A puzzlement |
| Real mystery |
| Brain teaser |
| Mind-boggler |
| Tough puzzle |
| It's puzzling |
| Hmm?" inducer |
| Brain-twister |
| Nazi's cipher |
| Total stumper |
| Hmm" provoker |
| It's not clear |
| It's a mystery |
| Head-scratcher |
| Baffling matter |
| Baffling person |
| Mysterious sort |
| Obscure saying. |
| Puzzling riddle |
| Cryptic mystery |
| Baffling puzzle |
| Riddle relative |
| Puzzling problem |
| Complete baffler |
| Riddle or puzzle |
| Inscrutable sort |
| Puzzling person? |
| Difficult problem |
| Mysterious puzzle |
| Baffling problem. |
| Perplexing puzzle |
| Tough nut to crack |
| Anything puzzling. |
| Inscrutable puzzle |
| Mysterious baffler |
| Challenging riddle |
| Inscrutable person |
| It's mind-boggling |
| It's no no-brainer |
| Hard nut to crack? |
| Puzzling situation |
| Hard-to-know person |
| Inexplicable puzzle |
| It's truly puzzling |
| WWII coding machine |
| Hard-to-crack puzzle |
| Mind-boggling puzzle |
| Reason to be at sea? |
| Russia, to Churchill |
| Woman's age, for one |
| It's hard to untangle |
| Something inscrutable |
| Something inexplicable |
| Something of a mystery |
| Contradictory character |
| Puzzle that's a stumper |
| Something hard to grasp |
| Tough one to figure out |
| WWII encryption machine |
| It's hard to figure out |
| It's hard to understand |
| Axis enciphering machine |
| Elgar's "____ Variations |
| Puzzling person or thing |
| Churchill word for Russia |
| Hard puzzle to figure out |
| The Imitation Game" machine |
| It's something of a mystery |
| The Mona Lisa's smile, e.g. |
| W.W. II German cipher machine |
| Riddle — German coding machine |
| Sadeness (Part I)" electronic band |
| Ciphering system cracked by Alan Turing |
| I'm a walking, talking ___": Larry David |
| Nazi cipher machine broken by the Allies |
| German cipher machine cracked by Alan Turing |
| National Puzzlers League newsletter, with "The |
| National Puzzlers' League publication, with The |
| Code broken in the 2014 biopic "The Imitation Game |
| Encryption machine featured in "The Imitation Game |
| Appropriately named monthly of the National Puzzlers' League, with "The |