(plural tough nuts to crack)
- Used other than as an idiom: see tough, nut, crack.
- (idiomatic) A problem that is challenging to solve.
- (idiomatic, by extension) A situation, person, group, etc. which is difficult to deal with.
- (idiomatic) A place, opportunity, etc. to which it is difficult to gain entry.
- An amount that is difficult to finance.