A difficult circumstance or problem.
A type of syllogism of the form "if A is true then B is true; if C is true then D is true; either A or C is true; therefore either B or D is true".
A circumstance in which a choice must be made between two or more alternatives that seem equally undesirable.
Offering to an opponent a choice between two (equally unfavorable) alternatives.
A problem that is challenging to solve.
Used other than figuratively or idiomatically: see hard, nut, crack.
A situation, person, group, etc. which is difficult to overcome or deal with.
A place, opportunity, etc. to which it is difficult to gain entry.
An amount that is difficult to finance.