The word tattletale is mostly used in the U.S. (in Britain it's more common to use telltale). It comes from the verb tattle, "report someone's wrongdoing." In the 16th century, you'd have called a tattletale a pickthank. These days, you can also use words like snitch or whistle-blower.

What do tattletale means?

: someone (such as a child) who tells secrets about what someone else has done : one who tattles : informer. Synonyms Example Sentences Learn More About tattletale.

Is it tattletale or Tattletail?

Somebody who reveals secrets—tattling, telling tales—is a tattle-tale, often spelled as one word: “tattletale.”