let

Etymology 1

From Middle English leten, læten, from Old English lǣtan (“to allow, let go, bequeath, leave, rent”), from Proto-West Germanic *lātan, from Proto-Germanic *lētaną (“to leave behind, allow”), from Proto-Indo-European *leh₁d- (“to let, leave behind”). Cognates Cognate with Scots lat, lete (“to let, leave”), North Frisian lete (“to let”), West Frisian litte (“to let”), Dutch laten (“to let, leave”), German lassen (“to let, leave, allow”), Swedish låta (“to let, allow, leave”), Icelandic láta (“to let”), Albanian lë (“to allow, let, leave”) and partially related to French laisser (“to let”).

verb

1. (transitive) To allow to, not to prevent (+ infinitive, but usually without to).
   After he knocked for hours, I decided to let him come in.
   He could not be let die of thirst there alone in the dark. 1971, Ursula K. Le Guin, The Tombs of Atuan
   The dirty secret of the internet is that all this distraction and interruption is immensely profitable. Web companies like to boast about […], or offering services that let you "stay up to date with what your friends are doing",[…]and so on. But the real way to build a successful online business is to be better than your rivals at undermining people's control of their own attention. 2013-06-21, Oliver Burkeman, “The tao of tech”, in The Guardian Weekly, volume 189, number 2, page 27
2. (transitive) To allow to be or do without interference; to not disturb or meddle with; to leave (someone or something) alone.
   Let me be!
3. (transitive) To allow the release of (a fluid).
   The physicians let about a pint of his blood, but to no avail.
4. (transitive) 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.
   Trailers for sale or rent, rooms to let, fifty cents. 1965, Roger Miller (lyrics and music), “King Of The Road”
5. (transitive) 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
6. (auxiliary, transitive) Used to introduce a first or third person imperative verb construction.
   Let's put on a show!
   Let us have a moment of silence.
   Let me just give you the phone number.
   Let P be the point where AB and OX intersect.
7. (transitive, obsolete except with know) To cause (+ bare infinitive).
   Can you let me know what time you'll be arriving?
8. 1818, John Keats, To—:

noun

1. The allowing of possession of a property etc. in exchange for rent.
   Then he says “You would call it a Good Let, Madam?” “O certainly a Good Let sir.” 1854, Charles Dickens, Christmas Stories, page 317

Etymology 2

From Middle English letten (“to hinder, delay”), from Old English lettan (“to hinder, delay”; literally, “to make late”), from Proto-West Germanic *lattjan, from Proto-Germanic *latjaną. Akin to Old English latian (“to delay”), Dutch letten, Old English læt (“late”). More at late, delay.

verb

1. (archaic) To hinder, prevent, impede, hamper, cumber; to obstruct (someone or something).
2. (obsolete) To prevent someone from doing something; also to prevent something from happening.
   & there was syr Mordred redy awaytynge vpon his londage to lette his owne fader to lāde vp the lande that he was kyng ouer. "And there was Sir Mordred ready awaiting upon his landing, to let his own father to land upon the land that he was king over." 1485, Thomas Malory, Le Morte Darthur Book XXI, Chapter ii, leaf 421r
3. (obsolete) To tarry or delay.
   And for that strake I would not let, / Another upon him soon I set, […] 1826, Early Metrical Tales; Including the History of Sir Egeir, Sir Gryme, and Sir Gray-Steill, Edinburgh, The History of Sir Eger, Sir Grahame, And Sir Gray-Steel, page 7

noun

1. An obstacle or hindrance.
2. (tennis) The hindrance caused by the net during serve, only if the ball falls legally.