①to control the size or number of something and prevent it from increasing
压缩，控制，限制…的规模。
②to be able to eat or drink something without vomiting
吃（或喝）下东西（而不吐）。

【例句】
I'm going to sleep, so will you try to keep the noise down?
我要睡觉了，你能不能不要太吵？
 
On the day after her operation she couldn't keep anything down.
手术的第二天，她吃什么都吐。