tattletale

Short definition from Wiktionary

Adjective

1. 1
   telltale; giveaway

Noun

1. 1
   One who tattles (reports others' wrongdoings), often a child seeking attention.
2. 2
   One who gossips, often for the sake of attention.

Verb

1. 1
   To act as a tattletale; to tell on; to give away, reveal, or expose.