a person who informs against another, esp. for money or other reward.

a person who informs or communicates information or news; informant.

noun

accuser , adviser , announcer , betrayer , blab , blabbermouth , canary , crier , deep throat , double-crosser , fat mouth , finger , fink , fork tongue , herald , informer , interviewer , journalist , messenger , nark , newsman , notifier , preacher , propagandist , rat , ratfink , singer , snake , sneak , snitcher , songbird , source , squealer , stool pigeon , stoolie , tattler , tattletale , tipster , weasel , informant , plant