keep down

verb6

1. •
   To restrain or control (a sound).

   • We must keep the noise down, or the neighbours will complain.
   • Keep it down in there! Some of us are trying to sleep!
2. •
   To cause not to increase or rise.

   • It is essential to keep the numbers down to avoid overcrowding.
3. •
   To repress.

   • The dictatorial state keeps down its dissidents very efficiently.
4. •
   To retain in the stomach without vomiting.

   • It is difficult to keep anything down when you have the flu.
5. •
   To lie low; to stay concealed by not standing up.

   • You had better keep down or they will see you.
6. •
   (no longer used) To refrain from using capital letters more than absolutely necessary.