If you let something happen , you allow it to happen without doing anything to stop or prevent it.
let in
If an object lets in something such as air , light, or water, it allows air, light, or water to get into it, for example because the object has a hole in it.
let off
If someone in authority lets you off a task or duty , they give you permission not to do it.
let on
If you do not let on that something is true , you do not tell anyone that it is true, and you keep it a secret.
let out
If something or someone lets water, air, or breath out , they allow it to flow out or escape.
let up
If an unpleasant , continuous process lets up , it stops or becomes less intense .
let down
If you let someone down , you disappoint them, by not doing something that you have said you will do or that they expected you to do.
let into
If you let someone into a secret, you allow them to know it.
let in on
If you let someone in on something that is a secret from most people, you allow them to know about it.
let through
to allow to pass (through)
let up on
If you let up on someone or something, you stop being so harsh or strict with them.