Dictionary.com
definitions

let

1
[let]
See more synonyms for let on Thesaurus.com
verb (used with object), let, let·ting.
  1. to allow or permit: to let him escape.
  2. to allow to pass, go, or come: to let us through.
  3. to grant the occupancy or use of (land, buildings, rooms, space, etc., or movable property) for rent or hire (sometimes followed by out).
  4. to contract or assign for performance, usually under a contract: to let work to a carpenter.
  5. to cause to; make: to let one know the truth.
  6. (used in the imperative as an auxiliary expressive of a request, command, warning, suggestion, etc.): Let me see. Let us go. Just let them try it!
verb (used without object), let, let·ting.
  1. to admit of being rented or leased: The apartment lets for $100 per week.
noun
  1. British. a lease.
Verb Phrases
  1. let down,
    1. to disappoint; fail.
    2. to betray; desert.
    3. to slacken; abate: We were too near success to let down in our efforts.
    4. to allow to descend slowly; lower.
    5. Aeronautics.(of an airplane) to descend from a higher to a lower altitude preparatory to making an approach and landing or a similar maneuver.
  2. let in,
    1. to admit.
    2. to involve (a person) in without his or her knowledge or permission: to let someone in for a loss.
    3. Also let into.to insert into the surface of (a wall or the like) as a permanent addition: to let a plaque into a wall.
    4. Also let in on.to share a secret with; permit to participate in.
  3. let off,
    1. to release by exploding.
    2. to free from duty or responsibility; excuse.
    3. to allow to go with little or no punishment; pardon: The judge let off the youthful offender with a reprimand.
  4. let on,
    1. to reveal one's true feelings: She was terrified at the prospect, but didn't let on.
    2. to pretend: They let on that they didn't care about not being invited, but I could tell that they were hurt.
  5. let out,
    1. to divulge; make known.
    2. to release from confinement, restraint, etc.
    3. to enlarge (a garment).
    4. to terminate; be finished; end: When does the university let out for the summer?
    5. to make (a let-out fur or pelt).
  6. let up,
    1. to slacken; diminish; abate: This heat wave should let up by the end of the week.
    2. to cease; stop: The rain let up for a few hours.
  7. let up on, to treat less severely; be more lenient with: He refused to let up on the boy until his grades improved.
Idioms
  1. let alone. alone(def 8).
  2. let be,
    1. to refrain from interference.
    2. to refrain from interfering with.
  3. let go. go1(def 93).
  4. let someone have it, Informal. to attack or assault, as by striking, shooting, or rebuking: The gunman threatened to let the teller have it if he didn't move fast.

Origin of let

1
before 900; Middle English leten, Old English lǣtan; cognate with Dutch laten, German lassen, Old Norse lāta, Gothic lētan; akin to Greek lēdeîn to be weary, Latin lassus tired. See late

Synonyms for let

See more synonyms for on Thesaurus.com
1. suffer, grant. 3. lease, rent, sublet, hire.

Synonym study

1. See allow.

Antonyms for let

1. prevent.

Usage note

Let us is used in all varieties of speech and writing to introduce a suggestion or a request: Let us consider all the facts before deciding. The contracted form let's occurs mostly in informal speech and writing: Let's go. Let's not think about that right now. Perhaps because let's has come to be felt as a word in its own right rather than as the contraction of let us, it is often followed in informal speech and writing by redundant or appositional pronouns: Let's us plan a picnic. Let's you and I (or me ) get together tomorrow. Both Let's you and me and Let's you and I occur in the relaxed speech of educated speakers. The former conforms to the traditional rules of grammar; the latter, nonetheless, occurs more frequently. See also leave1.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for let in on

educate, update, apprise, brief, warn, instruct, caution, notify, advise, tell, disclose, reveal, give, suggest, alert, declare, telephone, announce, fit, provide
British Dictionary definitions for let in on

let

1
verb lets, letting or let (tr; usually takes an infinitive without to or an implied infinitive)
  1. to permit; allowshe lets him roam around
  2. (imperative or dependent imperative)
    1. used as an auxiliary to express a request, proposal, or command, or to convey a warning or threatlet's get on; just let me catch you here again!
    2. (in mathematical or philosophical discourse) used as an auxiliary to express an assumption or hypothesislet "a" equal "b"
    3. used as an auxiliary to express resigned acceptance of the inevitablelet the worst happen
    1. to allow the occupation of (accommodation) in return for rent
    2. to assign (a contract for work)
  4. to allow or cause the movement of (something) in a specified directionto let air out of a tyre
  5. Irish informal to utterto let a cry
  6. let alone
    1. (conjunction)much less; not to mentionI can't afford wine, let alone champagne
    2. let be, leave alone or leave beto refrain from annoying or interfering withlet the poor cat alone
  7. let go See go 1 (def. 59)
  8. let loose
    1. to set free
    2. informalto make (a sound or remark) suddenlyhe let loose a hollow laugh
    3. informalto discharge (rounds) from a gun or gunsthey let loose a couple of rounds of ammunition
noun
  1. British the act of letting property or accommodationthe majority of new lets are covered by the rent regulations
See also let down, let in, let into, let off, let on, let out, let through, let up

Word Origin for let

Old English lǣtan to permit; related to Gothic lētan, German lassen

let

2
noun
  1. an impediment or obstruction (esp in the phrase without let or hindrance)
  2. tennis squash
    1. a minor infringement or obstruction of the ball, requiring a point to be replayed
    2. the point so replayed
verb lets, letting, letted or let
  1. (tr) archaic to hinder; impede

Word Origin for let

Old English lettan to hinder, from læt late; related to Old Norse letja
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for let in on

let

v.

Old English lætan "to allow to remain; let go, leave, depart from; leave undone; to allow; bequeath," also "to rent" (class VII strong verb; past tense let, past participle læten), from Proto-Germanic *letan (cf. Old Saxon latan, Old Frisian leta, Dutch laten, German lassen, Gothic letan "to leave, let"), from PIE *le- "to let go, slacken" (cf. Latin lassus "faint, weary," Lithuanian leisti "to let, to let loose;" see lenient). If that derivation is correct, the primary sense would be "let go through weariness, neglect."

Of blood, from late Old English. To let (something) slip originally (1520s) was a reference to hounds on a leash; figurative use from 1540s. To let (someone) off "allow to go unpunished" is from 1814. To let on "reveal, divulge" is from 1725; to let up "cease, stop" is from 1787. Let alone "not to mention" is from 1812.

let

n.

"stoppage, obstruction" (obsolete unless in legal contracts), late 12c., from archaic verb letten "to hinder," from Old English lettan "hinder, delay," from Proto-Germanic *latjanan (cf. Old Saxon lettian "to hinder," Old Norse letja "to hold back," Old High German lezzen "to stop, check," Gothic latjan "to hinder, make late," Old English læt "sluggish, slow, late"); see late.

Online Etymology Dictionary, © 2010 Douglas Harper
Idioms and Phrases with let in on

let in on

Allow someone to know about or participate in something, as in I'm going to let you in on a little secret. This idiom was first recorded in 1904.

let

In addition to the idioms beginning with let

  • let alone
  • let be
  • let bygones be bygones
  • let daylight through or into
  • let down
  • let down easy
  • let down one's hair
  • let drop
  • let fly
  • let go
  • let grass grow
  • let in on
  • let it all hang out
  • let it lay
  • let it rip
  • let me see
  • let off
  • let off steam
  • let on
  • let oneself go
  • let one's hair down
  • let out
  • let ride
  • let sleeping dogs lie
  • let slide
  • let slip
  • let someone
  • let someone down
  • let someone have it
  • let the cat out of the bag
  • let the chips fall where they may
  • let the grass grow under one's feet
  • let the side down
  • let up
  • let well enough alone

also see:

  • blow (let) off steam
  • give (let) someone have his or her head
  • (let someone) have it
  • live and let live

Also see underleave.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.