There are numerous synonyms for the word "coppers nark". Some of the commonly used synonyms are informer, snitch, rat, tattler, betrayer, stool pigeon, squealer, and grass. These words refer to a person who provides information to the police or authorities about the illegal activities of others. These words are often used in a negative context as such people are generally considered to be disloyal, untrustworthy and treacherous. While some people may consider such behavior to be necessary to maintain law and order, others believe that it goes against the principles of loyalty and trust. Therefore, it is important to use these words carefully and appropriately in order to avoid any unintentional offence or disrespect.