let alone, means not to mention; much less.是指更不用提；更别说的意思。例如：

Their ancestors had been dirt poor and never saw royalty, let alone hung around with them?

“他们的祖先穷得要命，从来没有见过王族成员，更不用说和他们在一起了”。

let go, means to cease to employ; dismiss.是指不再雇用；解雇的意思。例如：

had to let 20 workers go.

必须解雇二十名工人。

let off on, means to cause to diminish, as in pressure; ease up on.是指降低，如压力；缓和的意思。例如：

Let off on the gas so that we do not exceed the speed limit.

减小油门以防止超过限速。

let (one's) hair down, means to drop one's reserve or inhibitions.是指消除某人的拘谨或压抑的意思。

let up on, means to be or become more lenient with.是指较宽容地对待的意思。例如：

Why don't you let up on the poor child?

你为什么不能较宽容地对待这个可怜的孩子呢?

let's，这是我们最常用的。通常表示建议或命令。例如：

Let's go swimming on Sunday.

我们星期日去游泳吧！

Come on Mary, let's dance!

来吧！玛丽，我们来跳舞吧！

let the cat out of the bag，是指在不小心的情况下泻露了秘密的意思。