Tim Bowen has a crack at cracking the case of this useful word.

Apart from its usual meanings of ‘to break something so that a line appears on it’, ‘to break something open’ or ‘to hit something hard’, the transitive form of the verb crack can also mean to solve a complicated problem or find the answer to a mystery, as in ‘With the help of DNA, detectives believe they are finally close to cracking a case that has remained unsolved for twenty years’. 

If you crack a joke, you tell a joke, as in ‘He was very relaxed, smiling and cracking jokes’.

The intransitive form of the verb can mean to lose control of yourself and say or do things you wouldn’t normally say or do, because you are tired or have been threatened, as in ‘After several hours of questioning, the suspect finally cracked and admitted that he had masterminded the operation’. 

If your voice cracks, it goes higher and lower and you cannot control it, especially because of a strong emotion or because you are going to cry.

The noun crack has several meanings, one of which is ‘an attempt to do something’, as in ‘We thought we’d have a crack at running our own business’. 

Crack can also be used as an adjective, with the meaning of being very skilful, especially as a result of being trained well, as in ‘A crack team of soldiers has been sent in to attempt to rescue the hostages’. A crack shot is someone who is very accurate in shooting a gun, as in ‘She’s a crack shot with a rifle’.