英汉词典

1. 在整个夜间；在夜里的某一时刻
    If something happens overnight, it happens throughout the night or at some point during the night.

    e.g. The weather remained calm overnight...
           整晚都悄然无风。
    e.g. The decision was reached overnight...
           决定是在夜里作出的。

2. 突然；一下子；一夜之间
    You can say that something happens overnight when it happens very quickly and unexpectedly.

    e.g. The rules are not going to change overnight...
           这些规定不会说变就变。
    e.g. He's realistic enough to know he's not going to succeed overnight...
           他很现实，知道自己的成功不会一蹴而就。

3. 只供一两晚使用的
    Overnight bags or clothes are ones that you take when you go and stay somewhere for one or two nights.

    e.g. He realized he'd left his overnight bag at Mary's house.
           他意识到自己把过夜包落在玛丽家了。

4. 过夜
    If you overnight somewhere, you spend the night there.

    e.g. They had told her she would be overnighting in Sydney.
           他们跟她说过她将在悉尼过夜。