Synonyms for Telltale (same or very similar meaning)
WordNet sense 1 (someone who gossips indiscreetly):
blabbermouth, talebearer, tattler, tattletale, taletellerWordNet sense 2 (disclosing unintentionally):
revealing, tellingWordNet sense 3 (providing or conveying information):
informative, informatoryFrom the ODE community, based on WordNetadd/edit