police

The police are the government force who enforce laws, prevent crime, stop and arrest criminals, regulate traffic, help maintain public order, and help with emergencies.

Example: When we saw the man take the money, we called the police.

The police means the city government department that is concerned with enforcing laws and helping with emergencies.

Example: The Police Department there replaced the previous system of having volunteers keep the city safe.

If you police an area or activity, you watch it to make sure no laws are being broken.

Example: There are fewer crimes in the countryside, but it's difficult to police such a big area.