Benedict Arnold
Brutus
Judas
Judas Iscariot
Quisling
accusant
accuser
adviser
allegator
announcer
annunciator
appellant
archtraitor
attestant
attestator
attester
authority
betrayer
blab
blabber
blabberer
blabbermouth
bystander
canary
channel
claimant
cockatrice
cojuror
communicant
communicator
complainant
compurgator
conniver
conspirator
conspirer
delator
deponent
double agent
double-crosser
double-dealer
earwitness
enlightener
expert witness
eyewitness
fink
gossipmonger
grapevine
grass
impeacher
impugner
informant
source
Fink
copper's nark
nark
sneak
sneaker
snitch
snitcher
stool pigeon
stoolie
supergrass
alloit
bangladeshi
black-bodied
bold-faced
career-threatening
prevenir
uncalled
wage-earning
whizz-bang
dormer
former
performer
reformer
stormer
transformer
warmer