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

1.
morder a língua, segurar a língua
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.
Tive que morder a língua para não dizer o que realmente pensava.
•
She wanted to argue, but decided to bite her tongue.
Ela queria discutir, mas decidiu morder a língua.