Crossword Clue:

Inform on someone

AnswerCrossword Clue
RATInform (on)
TATTLEInform on.
BLOWTHEWHISTLEInform (on)
RATInform on
LET... in on (inform)
RATOUTInform on, slangily
RATInform on the Mob
RATInform on the mob
RATInform on, with "out"
SINGInform on a fellow-criminal: Slang.
SINGInform on partners in crime: Slang.