rat on
To tell someone in charge (like a teacher, boss, or police) about something bad another person did — especially someone you were supposed to be loyal to.
Meanings
To betray someone by reporting their activities to an authority.
"He ratted on his partners to the police in exchange for a lighter sentence."
To break a promise or agreement; to go back on one's word.
"The supplier ratted on the deal at the last minute, leaving us with nothing."
Always implies betrayal — the person ratting is breaking a code of loyalty. Very common in school, criminal, and workplace contexts. Slightly more British in tone than 'rat out.' The term comes from the idea of a rat as a sneaky, disloyal creature.
Commonly used with
Forms
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