1.rat用作名词时意思是“鼠”,转化为动词意为“捕鼠”,引申可表示“背叛”“告发”“食言”。
2.rat只用作不及物动词,在口语中常与介词on连用。
3.rat的过去式和过去分词均为ratted。

rat on(v.+prep.)
〈口〉背叛,告发; 食言 betray or inform on (sb); go back on (sth)
▲rat on sb/sth
That coward ratted on his fellow-workers.那个胆小鬼告发了和他一起干活的工人。
The police know we're here.Someone must have ratted on us.警察知道我们在这儿,一定是有人背叛了我们。
We shouldn't rat on our promise.我们不应该违背诺言。

用作不及物动词
▲S+～(+A)
The dogs went ratting.狗都去捕捉老鼠了。
They said they'd help us but they've ratted.他们答应帮助我们,但他们食言了。

［同义词］ n.  mouse
［词源］＜古英语ræt(鼠)

The rats have eaten holes in those bags of flour.大老鼠把那些面粉袋嗑出了窟窿。
He looks like a drowned rat.他看上去像一只落汤鸡,全身都湿透了。
But you promised to help us, you rat!可是你答应过要帮我们的忙,你这言而无信的小人!

rat, mouse
参见mouse条。