To allow to, not to prevent (+ infinitive, but usually without to).
After he knocked for hours, I decided to let him come in.
To leave.
Let me alone!
To allow the release of (a fluid).
The physicians let about a pint of his blood, but to no avail.
To allow possession of (a property etc.) in exchange for rent.
I decided to let the farmhouse to a couple while I was working abroad.
To give, grant, or assign, as a work, privilege, or contract; often with out.
to let the building of a bridge; to let out the lathing and the plastering
Used to introduce an imperative in the first or third person.
Let P be the point where AB and OX intersect.
To cause (+ bare infinitive).
Can you let me know what time you'll be arriving?
To hinder, prevent, impede, hamper, cumber; to obstruct (someone or something).
To prevent someone from doing something; also to prevent something from happening.
To tarry or delay.