If you let something happen, you allow it to happen without doing anything to stop or prevent it.

If you let someone do something, you give them your permission to do it.

If you let someone into, out of, or through a place, you allow them to enter, leave, or go through it, for example by opening a door or making room for them.

You use let me when you are introducing something you want to say.

You use let me when you are offering politely to do something.

You say let's or, in more formal English, let us, to direct the attention of the people you are talking to towards the subject that you want to consider next.

You say let's or, in formal English, let us, when you are making a suggestion that involves both you and the person you are talking to, or when you are agreeing to a suggestion of this kind.

Someone in authority, such as a teacher, can use let's or, in more formal English, let us, in order to give a polite instruction to another person or group of people.

People often use let in expressions such as let me see or let me think when they are hesitating or thinking of what to say next.

You can use let to say that you do not care if someone does something, although you think it is unpleasant or wrong.

You can use let when you are saying what you think someone should do, usually when they are behaving in a way that you think is unreasonable or wrong.

You can use let when you are praying or hoping very much that something will happen.

You can use let to introduce an assumption on which you are going to base a theory, calculation, or story.

If you let your house or land to someone, you allow them to use it in exchange for money that they pay you regularly.

In tennis or badminton, if you serve a let, the ball or shuttlecock touches the net but lands in the correct part of the court. You then serve again.

Let alone is used after a statement, usually a negative one, to indicate that the statement is even more true of the person, thing, or situation that you are going to mention next.

To let someone be means to leave them alone and not interfere in what they are doing.

If you let go of someone or something, you stop holding them.

If you let go of a feeling, attitude, or the control that you have over something, you accept that you should give it up or that it should no longer influence you.

If you let someone or something go, you allow them to leave or escape.

When someone leaves a job, either because they are told to or because they want to, the employer sometimes says that they are letting that person go .

If someone says or does something that you think is annoying or stupid and you let it go, you do not react to it or say anything about it.

If you let yourself go, you relax and behave much more freely than usual.

If someone lets themselves go, they pay less attention to themselves or their appearance than they used to, so that they look untidy or unattractive.

If you say that you did not know what you were letting yourself in for when you decided to do something, you mean you did not realize how difficult, unpleasant, or expensive it was going to be.

If you let someone know something, you tell them about it or make sure that they know about it.

If you let drop ,let fall, or let slip information, you reveal it casually or by accident, during a conversation about something else.

If you say that someone has been let loose in a place or situation, you mean that they have been given complete freedom to do what they like in that place or situation, and you suggest that this may be risky.

If someone lets loose a sound or remark, they make it, often suddenly.

If something lets you down, it is the reason you are not as successful as you could have been.

If you let down something such as a tyre, you allow air to escape from it.