Narc is a slang term that refers to a law enforcement officer or a person who informs to the authorities about criminal activities. It is a derogatory word and is often used to describe someone who is untrustworthy or a snitch. There are several synonyms for the word narc, including informer, rat, snitch, stool pigeon, and informant, among others. These words are also slang terms and are generally used to describe someone who provides information to the authorities about unlawful activities. However, these terms should be used with caution as they can be considered offensive and disrespectful to law enforcement officers.