1. (Figuré) Personne froide, endurcie.
2. [noun] Used other than as an idiom: see hard,? nut,? crack.
3. [noun] (idiomatic) A problem that is challenging to solve.
4. [noun] (idiomatic) (by extension) A situation, person, group, etc. which is difficult to overcome or deal with.
5. [noun] (idiomatic) A place, opportunity, etc. to which it is difficult to gain entry.
6. [noun] (idiomatic) An amount that is difficult to finance.
