hard nut to crack

• harder nut to crack, hardest nut to crack
• difficult nut to crack, tough nut to crack

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hard nut to crack (plural hard nuts to crack)

1. Used other than with a figurative or idiomatic meaning: see hard,‎ nut,‎ crack.
2. (idiomatic) A problem that is challenging to solve.
   • 1893, Grant Allen, chapter 11, in Michael's Crag:

     He saw the dilemma. . . . It was a hard nut to crack. He could see no way out of it.

   • 1991 June 14, Leonard Silk, "Economic Scene; Predicting When Upturn Will Start," New York Times (retrieved 22 Sep. 2011):

     Germany's inflation proves a hard nut to crack.

3. (idiomatic, by extension) A situation, person, group, etc. which is difficult to overcome or deal with.
   • 1928 June 8, "Mike McTigue Gives Emanuel a Real Fight," Milwaukee Journal, p. 2 (retrieved 22 Sep. 2011):

     The coast lad found the veteran Mike McTigue a hard nut to crack and judging from the look on the Californian's face when the final bell sounded, he was mighty happy that the fight was over.

   • 2011 Jan. 12, Simon Shuster, "Will the E.U. Let Belarus' Despot Off the Hook?," Time:

     "But Belarus is a hard nut to crack, and it has used these methods to slip out of these East-West pincers before," says Alexander Klaskovsky.

4. (idiomatic) A place, opportunity, etc. to which it is difficult to gain entry.
   • 1885, G. A. Henty, chapter 7, in In Freedom's Cause:

     The next day Archie, with Andrew Macpherson and Cluny Campbell, made their way through the woods until within sight of the castle. . . .

     "It would be a hard nut to crack, Sir Archie," his lieutenant said. "Unless by famine, the place could scarce be taken."

   • 1929 March 15, "Five Mexican Armies March to Meet Rebels," Reading Eagle (USA), p. 1 (retrieved 22 Sep. 2011):

     Durango, however, may be a hard nut to crack, as it is strong strategically and is reported guarded by 4000 rebels.

   • 2008 Oct. 17, Barbara Wall, "Housing crisis? Not for the superrich," New York Times (retrieved 22 Sep. 2011):

     Nice work if you can get it, but the luxury market is a hard nut to crack.

5. (idiomatic) An amount that is difficult to finance.

• Tough/er/est nut to crack is by far the most common form in COCA (US), about equal to hard/er/est nut to crack at BNC (UK).