1. 老鼠;耗子
    A rat is an animal which has a long tail and looks like a large mouse.

rat在线翻译

    e.g. This was demonstrated in a laboratory experiment with rats.
           在实验室用老鼠进行的实验证明了这一点。
    e.g. ...a rat-infested derelict building.
           鼠灾泛滥的废弃建筑

2. 卑劣的人；不忠实的人；小人
    If you call someone a rat, you mean that you are angry with them or dislike them, often because they have cheated you or betrayed you.

    e.g. What did you do with the gun you took from that little rat Turner?
           你是怎么处理从那个叫特纳的小叛徒手里得到的枪的？

3. 告密;出卖
    If someone rats on you, they tell someone in authority about things that you have done, especially bad things.

    e.g. They were accused of encouraging children to rat on their parents.
           他们被指控唆使儿童告发自己的父母。

4. 违约；食言
    If someone rats on an agreement, they do not do what they said they would do.

    e.g. She claims he ratted on their divorce settlement.
           她声称他违反了他们的离婚协议。

5. 怀疑有问题；发现不对头；有所警觉
    If you smell a rat, you begin to suspect or realize that something is wrong in a particular situation, for example that someone is trying to deceive you or harm you.

    e.g. If I don't send a picture, he will smell a rat...
           如果我不寄出照片，他将有所察觉。
    e.g. Though Lloyd George's behaviour seemed curious, Haig still did not smell a rat.
           尽管劳埃德·乔治的行为古怪，黑格仍然没有任何怀疑。