tattletale n.

late 15c., "to stammer, prattle," in Caxton's translation of "Reynard the Fox," probably from Middle Flemish tatelen "to stutter," parallel to Middle Dutch, Middle Low German, East Frisian tateren "to chatter, babble," possibly of imitative origin. The meaning "tell tales or secrets" is first recorded 1580s. Sense influenced by tittle. Related: Tattled; tattling. As a noun from 1520s. Tattler, the name of the famous periodical by Addison and Steele (1709-1711), means "idle talker, a gossip."

Old English talu "series, calculation," also "story, tale, statement, deposition, narrative, fable, accusation, action of telling," from Proto-Germanic *talō (source also of Dutch taal "speech, language," Danish tale "speech, talk, discourse," German Erzählung "story," Gothic talzjan "to teach"), from PIE root *del- (2) "to recount, count." The secondary Modern English sense of "number, numerical reckoning" (c. 1200) probably was the primary one in Germanic; see tell (v.), teller and Old Frisian tale, Middle Dutch tal, Old Saxon tala, Danish tal, Old High German zala, German Zahl "number."

The ground sense of the Modern English word in its main meaning, then, might have been "an account of things in their due order." Related to talk (v.) and tell (v.). Meaning "things divulged that were given secretly, gossip" is from mid-14c.; first record of talebearer "tattletale" is late 15c.