保持沉默
to say nothing about a subject
It's not official yet, so keep mum. 这还不是正式的，所以不要讲出去。
The actors were romantically involved for several years, but preferred to keep mum on the subject.
She was told to keep mum about what she had seen.
They're keeping mum about the exact date of the baby's arrival.
For now, he's keeping mum on his plans for the future.
Synonym: silent
See also: mum adjective