informant (n.)

• adviser
• announcer
• annunciator
• attestant
• attestator
• attester
• authority
• bystander
• channel
• communicant
• communicator
• deponent
• examinee
• eyewitness
• gossipmonger
• grapevine
• informer
• interviewee
• monitor
• mouthpiece
• newsmonger
• passerby
• press
• publisher
• radio
• reporter
• source
• spectator
• spokesman
• subject
• swearer
• television
• teller
• testifier
• tipster
• tout
• voucher
• witness