$1,000,000 question

Noun

million-dollar question (plural million-dollar questions)

1. (figuratively) A question that is very important, difficult to answer, or (especially) both.
   • Newfoundland claims on western Labrador rest largely on old regulations for the fur industry. The new official boundary strikes north from Belle Isle Straits, turns west at 52° latitude for 300 miles and then weaves north toward Cape Chidley, encompassing on the way headwaters of all rivers...1927 March 28, “Where the New Boundary Runs”, in Geographic News Bulletin, volume 6, number 5, page 1

   Synonyms:

   sixty-four dollar question, sixty-four thousand dollar question, billion-dollar question

2. Used other than figuratively or idiomatically: a question to be decided, on whose answer depends a million-dollar expenditure.
   • National Assn. of City Editors—One faction views with alarm the proposal of President Clyde P. Steen that the association raise a fund of $1,000,000 to fight Bolshevism. The opponents of Mr. Steen claim that city editors have enough to do without the additional responsibility and troubles of a...1920 January 17, “Onward march of organization. Many organizations of newspaper men revive activities temporarily shut off by war”, in The Fourth Estate: A Weekly Newspaper for Publishers...