keep down

To repress.

“China keeps down her dissidents very efficiently.”

To restrain or control (a sound).

“Keep it down in there! Some of us are trying to sleep!”

To cause not to increase or rise.

“It is essential to keep the numbers down to avoid overcrowding.”

Not to vomit.

“It is difficult to keep anything down when you have the flu.”

To lie low. To stay concealed by not standing up

“You had better keep down or they will see you.”