bite your tongue
US /baɪt jʊər tʌŋ/
UK /baɪt jʊər tʌŋ/

1.
mordre sa langue, se retenir de parler
to make a conscious effort to avoid saying something that you want to say, often because it would be inappropriate or cause trouble
:
•
I had to bite my tongue to keep from telling him what I really thought.
J'ai dû mordre ma langue pour ne pas lui dire ce que je pensais vraiment.
•
She wanted to argue, but decided to bite her tongue.
Elle voulait discuter, mais a décidé de mordre sa langue.