These words refer to people who divulge facts to which they are privy. Among its extremely informal or slangy companions, informer seems formal and dignified by comparison; it is also more general than the others. It often suggests divulging secrets or information concerning illegal or scandalous behaviour: turning informer on his cronies in the crime syndicate; encouraging children to act as informers against their parents. The disclosure itself may be covert or open and may be given out of vengeance, self-interest, or for pay. The informer may decide to disclose information he acquired in good faith, or he may have been intent at the outset on gaining and then betraying someone’s confidence: an informer planted by the police to get evidence on a suspected narcotics ring; publicly turning informer at the hearing to clear himself of a charge of complicity. The disapproving tone that informer can give is milder than that of any other word here. It can even have a neutral or approving tone: a Nazi who turned informer to help the prosecutors at the Nuremberg trials.

Blabbermouth , by contrast, seldom suggests covert disclosure done in reprisal or self-interest. Instead, the word indicates general loose-Mouthed behaviour in someone willing to talk to anyone about anything, his own secrets as much as those of others: a blabbermouth who betrays his friends daily without even being conscious of it.

Tattler , talebearer and tattletale all can be used to describe someone who divulges facts about someone else. Each, however, has its special area of relevance. Tattler in particular relates to the collecting and spreading of trivial gossip of a faintly scandalous nature: professional tattlers who purport to reveal the private lives of the Hollywood stars. It may also suggest the situation in which one child betrays his playmates to a teacher, parent or other outsider; tattletale is perhaps more clearly related and restricted to such a context: the tattletale who went whining to the teacher about who had hidden the blackboard duster. Talebearer suggests to inform each side exclusively about the other: labour mediators who lose their effectiveness as soon as either side suspects them of being talebearers .

Fink once was restricted to a U.S. labour context as an extremely pejorative way to refer to a turncoat who willingly informed on his follow workers to their employer. It and the more current ratfink are now fad words referring to anyone who is unsavoury, contemptible, ridiculous or inconsequential: the fink who stole my pencil; He acts tough, but in my book he’s just a spineless fink ; My landlord is a real ratfink .

Squealer and stool pigeon are the most slangy and also the most pejorative words in this group; both may suggest a context of the criminal underworld but are widely used outside it. Squealer may refer to someone who divulges facts about his confederates for whatever reason: swearing that he’d never be a squealer no matter how long the police questioned him. Stool pigeon , by contrast, refers specifically to a covert informer who inhabits the underworld or is planted there by the police: in either case, he furtively continues to convey information to the police so long as he remains undiscovered: convinced that one of their fellow prisoners had turned stool pigeon and had disclosed their plans for the gaolbreak.