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

1.
morderse la lengua, callarse
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.
Tuve que morderme la lengua para no decirle lo que realmente pensaba.
•
She wanted to argue, but decided to bite her tongue.
Quería discutir, pero decidió morderme la lengua.