Synonyms: inform (on), grass (on), sneak (on)
inform on sb: to give information to the police or sb in authority about the illegal activities of sb 告发，检举
He informed on his own brother.
他告发了自己的亲弟弟。
Grass on sb: to tell the police about sb's criminal activities (向警方)告密，告发
Sneak on sb: (儿童向成人)打小报告，告状
Did you sneak on me to the teacher?
你有没有向老师告我的状？