1 B1 idiomatic informal
To betray someone by reporting their activities to an authority.
"He ratted on his partners to the police in exchange for a lighter sentence."
inseparable
rat on
B1 informal inseparable transitive
To secretly inform on someone to an authority, especially betraying a friend or associate.
In plain English
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.
What does "rat on" mean?
2 meanings, ordered from most common to least. Color-coded by CEFR level.
2 B2 idiomatic informal
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."
inseparable
Literal vs figurative
Words literally mean
Behaving like a rat — an animal associated with abandoning a sinking ship and with disloyalty.
Actually means
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.
Usage tip
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.
Words that pair with "rat on"
Natural word combinations native speakers use most often.
friend colleague partner boss police teacher
How to conjugate "rat on"
The five tense forms you'll use most often.
Base
rat on
I/you/we/they
3rd person
rats on
he/she/it
Past simple
rated on
yesterday
Past participle
rated on
have + pp
-ing form
rating on
continuous
Hear "rat on" in the wild
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