tell tales (third-person singular simple present tells tales, present participle telling tales, simple past and past participle told tales) (idiomatic) To lie, to be making false claims. Don't listen to him; he's telling tales. (UK) To report someone for a wrongdoing.

Divulge secrets, as in Don't trust him; he's apt to tell tales. This expression was first recorded about 1350. A variant, tell tales out of school, first recorded in 1530, presumably alluded to schoolchildren gossiping but was soon broadened to revealing secret or private information. Both may be obsolescent.