A problem, or unpleasant or painful situation or person that you have to accept and deal with, although you find it very difficult, or it causes trouble or worry for you over a long period of time.
A situation, person, group, etc. which is difficult to overcome or deal with.
A problem that is challenging to solve.
Used other than figuratively or idiomatically: see hard, nut, crack.
A place, opportunity, etc. to which it is difficult to gain entry.
An amount that is difficult to finance.