rat2 past tense and past participle ratted, present participle ratting [intransitive] informal
if someone rats on you, they tell someone in authority about something wrong that you have done [= grass on]
They'll kill you if they find out you've ratted on them!
2 British English
to not do what you had promised to do [= go back on, renege on]
He accused the government of ratting on its promises to the disabled.
rat somebody ↔ out
You can't rat out your teammates.