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.
Anything that is difficult to understand or make sense of.
A riddle.
The state of being puzzled; perplexity.
A game for one or more people that is more or less difficult to work out or complete.
A jigsaw puzzle.
A crossword puzzle.
To think long and carefully, in bewilderment.
To perplex, confuse, or mystify; to cause (someone) to be faced with a mystery, without answers or an explanation.
To make intricate; to entangle.