noun

1. One who divulges private information with intent to hurt others.

2. Tattletale; squealer.

3. An indicator, such as a warning light, that serves to warn of a hazard or problem.

Synonyms: blabbermouth, gossip, rumormonger, talebearer

adjective

1. Revealing something, especially something not intended to be known.

   “He blushed when he approached, a telltale sign that he was happy to see him.”