Idiom: Break a leg

This is an idiom. It has a special meaning that is different to the ordinary meaning of each separate word.

It is used in several situations, but basically to wish luck to someone who is going to perform in a theater (some people believe that if you say “good luck” to an actor or performer, you bring them back luck).

For example, «I know you play an important part in A Street Car Named Desire tonight so, I wanted to say ‘break a leg’.»

There are more idioms with the word ‘leg’, for example, ‘to cost an arm and a leg’ which means to cost a lot of money. Can you think of any others?