run in
B2 informal separable transitive
In simple words
When police take you to the station, or when you drive a new car gently at first so the engine works well
Literal meaning: To run into a place — the police sense relates to bringing someone into the station
Meanings
1 B2
idiomatic
informal
(British, informal) To arrest someone and take them to a police station
"The officer threatened to run him in if he didn't calm down."
Grammar: separable
2 C1 neutral
To operate a new engine or machine gently and carefully at first so it functions correctly over time
"You should run in a new car by keeping the revs low for the first thousand miles."
Grammar: separable
Usage notes
The arrest sense is informal British English. The engine sense ('running in' a car) is becoming less common as modern engines require less careful breaking in.
Commonly used with
police engine car suspect arrest gearbox
Forms
Base
run in
I/you/we/they
3rd person
runs in
he/she/it
Past simple
ran in
yesterday
Past participle
run in
have + pp
-ing form
running in
continuous
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