1) Act the rat fink 2) Act the snitch 3) Be a fink 4) Be a rat fink 5) Be a ratfink 6) Be a snitch 7) Be a stoolie 8) Be a teller 9) Blab 10) Chatter aimlessly 11) Disclosure 12) Divulge a secret 13) Give things away 14) Gossip 15) Gossip, idle chatter 16) Inform to Mom 17) Play the informer 18) Rat out your brother 1) Blab 2) Blither 3) Blow a whistle 4) Point a finger 5) Rat 6) Sing like a canary 7) Tell 8) Tell on 
• (v. i.) To prate; to talk idly; to use many words with little meaning; to chat. • (v. i.) To tell tales; to communicate secrets; to be a talebearer; as, a tattling girl. • (n.) Idle talk or chat; trifling talk; prate.
Tat'tle intransitive verb [ imperfect & past participle Tattled ; present participle & verbal noun Tattling .] [ Akin to Middle English tateren , LG. tateln , Dutch tateren to stammer, and perhaps to English titt...Tat'tle noun Idle talk or chat; trifling talk; prate. « [ They] told the tattle of the day.» Swift. 
[n] - disclosing information or giving evidence about another
noun disclosing information or giving evidence about another