Informer (noun)

1. A person who provides information or tells secrets, especially to the police or other authorities.
2. A person who gives information or evidence against someone, especially in a criminal case.

Origin:

The word "informer" comes from the verb "inform" which means to provide knowledge or information.

Examples:

1. He was arrested as a result of information provided by an informer.
2. The informer was paid for providing information about the criminal activities.
3. The police relied on the informer to help them make an arrest.
4. The informer was placed in the criminal organization to gather information.
5. The informer's testimony was crucial in the conviction of the criminal.