英语短语：Be (as) thick as thieves 亲密无间

表达 “be as thick as thieves” 的意思和偷东西并无关连，而是用来形容友人关系密切、亲密无间，彼此间没有隔阂或秘密。这个表达通常用来暗示两人或多人就像 “thieves（小偷）” 聚在一起做坏事一样 “thick（密集地）”，悄悄地盘算或谈论不可告人的事情。

在使用时，可以去掉表达中的第一个 “as”，即 “be thick as thieves”，意思相同。
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例句
My daughter and her friend are thick as thieves and spend all their free time together. We often have no idea what they are up to, but they really enjoy themselves.
我女儿和她的朋友紧密无间，所有空闲时间都呆在一起。我们通常不知道她们在做什么，但她们确实玩得很开心。

The kids are as thick as thieves today. Whilst I was just on the phone they painted their faces with lipstick. They just looked at me as if nothing had happened!
孩子们今天真是相处得特别好。就在我打电话的时候，他们用口红在脸上画画。他们看着我，就像什么事情都没有发生一样！

Jack and Jim were as thick as thieves when they were younger, but when they went to university in different towns it just wasn’t the same.
杰克和吉姆年轻的时候亲密无间，但当他们去不同的城市上大学后，两人的关系就变了。