A person who provides information about criminal activities to law enforcement authorities. The police relied on an informer to gather evidence against the drug cartel.
A software tool or utility that supplies users with detailed information about a system or application. The new system informer displays real-time CPU and memory usage.
Historical, chiefly British law: a person who lays an information in court and prosecutes the offence, often for a share of the penalty. In the 18th century an informer could profit handsomely by initiating proceedings against smugglers.