Synonyms for Sixty-four-thousand-dollar question:

• n.

  •burning question (noun)
  • burning-question,
  • knotty questions.
  •difficult question (noun)
  • burning question.
  •mystery (noun)
  • braintwisters,
  • in-scrutabilities,
  • re buses,
  • abstrusenesses,
  • in-scrutability,
  • tough nut crack,
  • in scrutability,
  • mindbogglers,
  • sphinges,
  • in scrutabilities,
  • re-buses,
  • sixty four thousand dollar question,
  • inscrutabilities,
  • closed books,
  • inscrutablenesses.
  •very crucial question (noun)
  • million-dollar question,
  • crucial question.

• Other synonyms:

  •n.
  • abstruseness,
  • closed book,
  • grabber,
  • inscrutability,
  • mystery,
  • perplexity,
  • puzzler,
  • rebus,
  • rune,
  • sphinx,
  • stumper,
  • subtlety,
  • teaser,
  • thriller,
  • whodunit,
  • Inscrutableness,
  • Rebuses,
  • brainteaser,
  • brainteasers,
  • teasers,
  • grabbers,
  • whodunits,
  • occults,
  • thrillers,
  • runes,
  • braintwister,
  • chillers,
  • knotty question,
  • mindboggler,
  • sphinxes,
  • stumpers,
  • tough nut to crack,
  • vexed question,
  • vexed questions.