Definition of inform on

The phrase "inform on" has its roots in the criminal underworld of the late 19th century, specifically in the context of the mafia-like gangs that dominated urban areas in America at the time. When criminal organizations began to proliferate in major cities, law enforcement authorities discovered that they needed a way to gain intelligence about these groups without infiltrating them directly. They turned to informants, people who were already involved in criminal activities and who could provide them with inside information in exchange for lenient treatment or protection from prosecution. The term "informant" eventually gave rise to the phrase "inform on," which is compounded of the words "inform" (meaning to provide information) and "on" (meaning to report or testify). The result is a expression that is commonly used today in both criminal and non-criminal contexts to describe an action that involves sharing information with an authority figure or third party. Interestingly, the concept of informants is not unique to the English-speaking world. Similar practices can be found in other cultures, such as the Japanese term "chisanbōshi," which roughly translates to "grass-eating thief" — a term given to criminals who trade information to the police for reduced sentences. This highlights the universality of the idea of using informants to gain vital intelligence and underscores its important role in criminal investigation and beyond.