tough proposition

45 Moby Thesaurus words for "tough proposition":
      Augean task, Chinese puzzle, Herculean task, backbreaker,
      baffling problem, ballbuster, bitch, brain twister, chore,
      crossword puzzle, crux, dead lift, enigma, enigmatic question,
      floorer, handful, hard job, hard pull, heavy sledding,
      jigsaw puzzle, knot, knotty point, large order, man-sized job,
      mind-boggler, mystery, nut to crack, perplexed question,
      perplexity, poser, problem, puzzle, puzzlement, puzzler, question,
      question mark, rough go, sixty-four dollar question, sticker,
      stumper, tall order, tough job, uphill work, vexed question, why