hush up
hush up {v.}
1. To keep news of (something) from getting out; prevent people from knowing about.
It isn't always easy to hush up a scandal.
2. {informal}
To be or make quiet; stop talking, crying, or making some other noise. — Often used as a command.
"Hush up," Mother said, when we began to repeat ugly gossip.
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Source: A Dictionary of American Idioms