policeman

A policeman is a man whose job is enforcing the law. Uniform, radio, and a great deal of paperwork.

The word is giving way to police officer, which covers everybody, and to the informal officer as a form of address. Policewoman exists and is used less than it was, for the same reason. British English has a long list of informal terms, of which bobby is the friendliest and comes from Robert Peel, who founded the Metropolitan Police. The force collectively is simply the police, which takes a plural verb.