conundrum

kəˈnʌndrəm/

noun

1. a confusing and difficult problem or question.

   "one of the most difficult conundrums for the experts"

   synonyms:

   problem, difficult question, vexed question, difficulty, quandary, dilemma; More

   • a question asked for amusement, typically one with a pun in its answer; a riddle.

     synonyms:

     riddle, puzzle, word game, anagram; More