v.must not的缩写;不得;
例句:
You are valuable to the organization, you mustn't take chances.
组织上对你很器重, 你不得掉以轻心.
We mustn't catch the speaker up by so many questions.
我们不该用这么多问题来打断发言人.
This is a high precision job . There mustn't be the slightest slip.
这可是细活,不能有一星半点差错.