Let

Let is a word with several distinct senses and uses in English and in technical contexts. In everyday English, let is a verb meaning to allow or permit something to happen, as in “Let him speak.” It can appear in negative and emphatic forms, as in “Let it be” or “Let me go.” The sense of hindering or obstructing is archaic but survives in fixed phrases such as “without let or hindrance,” where let means obstruction.

In British English, let has a specialized meaning related to renting property. To let a property means to rent it out to a tenant; the item for rent may be described as “to let.” The owner or landlord is the lessor, while the person who rents is the tenant.

In mathematics and logic, let is used to introduce a variable or assumption, such as “Let x be a real number.” It helps define the scope of a proof or construction and is common in both informal explanations and formal write-ups.

In computing and programming, let is a keyword used to declare variables and bind values, often with specific scoping rules. Languages such as JavaScript, TypeScript, Rust, and many functional languages use let to introduce a new binding or binding block.

LET also stands for Linear Energy Transfer, an acronym used in radiation physics to describe the amount of energy deposited by ionizing radiation per unit distance traveled in matter.

Other uses include as a surname, in place names, or in various acronyms and titles. The core senses of let—permit, lease, introduce variables, and technical abbreviations—span language, law, mathematics, and science.