Meaning of “rat on sb/sth” in the English Dictionary

british dictionary

"rat on sb/sth" in British English

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rat on sb/sth

phrasal verb with rat uk /ræt/ us /ræt/ verb slang disapproving

to not be loyal to someone, especially by giving away secret information about them, or to fail to do something that you said you would do:

He ratted on us.
They ratted on the deal.

(Definition of “rat on sb/sth” from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)