A more thorough explanation:

A delator (pronounced di-lay-tuh-r) is a term from Roman law that refers to an informer or accuser. In particular, a delator was someone who made a habit of informing on and prosecuting others, especially for financial crimes.

Originally, this practice was encouraged, but later on, the delator became subject to the death penalty. The plural form of delator is delatores.

• A delator might report a neighbor for not paying their taxes.
• In ancient Rome, delatores were often motivated by the promise of a reward for their information.
• During the reign of Emperor Nero, delatores were used to root out political dissidents and enemies of the state.

These examples illustrate how a delator was someone who would inform on others for personal gain or to curry favor with those in power. They were often seen as untrustworthy and were eventually punished for their actions.