The Collaborative International Dictionary of English v.0.48:

-let \-let\ (-l[e^]t) suff. [From two French dim. endings -el
   (L. -ellus) and -et, as in bracelet.]
   A noun suffix having a diminutive force; as in streamlet,
   wavelet, armlet.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Let \Let\ (l[e^]t), v. t. [OE. letten, AS. lettan to delay, to
   hinder, fr. l[ae]t slow; akin to D. letten to hinder, G.
   verletzen to hurt, Icel. letja to hold back, Goth. latjan.
   See Late.]
   To retard; to hinder; to impede; to oppose. [Archaic]
   [1913 Webster]

         He was so strong that no man might him let. --Chaucer.
   [1913 Webster]

         He who now letteth will let, until he be taken out of
         the way.                                 --2. Thess.
                                                  ii. 7.
   [1913 Webster]

         Mine ancient wound is hardly whole,
         And lets me from the saddle.             --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Let \Let\, n.
   1. A retarding; hindrance; obstacle; impediment; delay; --
      common in the phrase without let or hindrance, but
      elsewhere archaic. --Keats.
      [1913 Webster]

            Consider whether your doings be to the let of your
            salvation or not.                     --Latimer.
      [1913 Webster]

   2. (Lawn Tennis) A stroke in which a ball touches the top of
      the net in passing over.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Let \Let\, v. t. [imp. & p. p. Let (Letted (l[e^]t"t[e^]d),
   [Obs].); p. pr. & vb. n. Letting.] [OE. leten, l[ae]ten
   (past tense lat, let, p. p. laten, leten, lete), AS.
   l[=ae]tan (past tense l[=e]t, p. p. l[=ae]ten); akin to
   OFries. l[=e]ta, OS. l[=a]tan, D. laten, G. lassen, OHG.
   l[=a]zzan, Icel. l[=a]ta, Sw. l[*a]ta, Dan. lade, Goth.
   l[=e]tan, and L. lassus weary. The original meaning seems to
   have been, to let loose, let go, let drop. Cf. Alas,
   Late, Lassitude, Let to hinder.]
   1. To leave; to relinquish; to abandon. [Obs. or Archaic,
      except when followed by alone or be.]
      [1913 Webster]

            He . . . prayed him his voyage for to let.
                                                  --Chaucer.
      [1913 Webster]

            Yet neither spins nor cards, ne cares nor frets,
            But to her mother Nature all her care she lets.
                                                  --Spenser.
      [1913 Webster]

            Let me alone in choosing of my wife.  --Chaucer.
      [1913 Webster]

   2. To consider; to think; to esteem. [Obs.] --Chaucer.
      [1913 Webster]

   3. To cause; to make; -- used with the infinitive in the
      active form but in the passive sense; as, let make, i. e.,
      cause to be made; let bring, i. e., cause to be brought.
      [Obs.]
      [1913 Webster]

            This irous, cursed wretch
            Let this knight's son anon before him fetch.
                                                  --Chaucer.
      [1913 Webster]

            He . . . thus let do slay hem all three. --Chaucer.
      [1913 Webster]

            Anon he let two coffers make.         --Gower.
      [1913 Webster]

   4. To permit; to allow; to suffer; -- either affirmatively,
      by positive act, or negatively, by neglecting to restrain
      or prevent.
      [1913 Webster]

   Note: In this sense, when followed by an infinitive, the
         latter is commonly without the sign to; as to let us
         walk, i. e., to permit or suffer us to walk. Sometimes
         there is entire omission of the verb; as, to let [to be
         or to go] loose.
         [1913 Webster]

               Pharaoh said, I will let you go.   --Ex. viii.
                                                  28.
         [1913 Webster]

               If your name be Horatio, as I am let to know it
               is.                                --Shak.
         [1913 Webster]

   5. To allow to be used or occupied for a compensation; to
      lease; to rent; to hire out; -- often with out; as, to let
      a farm; to let a house; to let out horses.
      [1913 Webster]

   6. To give, grant, or assign, as a work, privilege, or
      contract; -- often with out; as, to let the building of a
      bridge; to let out the lathing and the plastering.
      [1913 Webster]

   Note: The active form of the infinitive of let, as of many
         other English verbs, is often used in a passive sense;
         as, a house to let (i. e., for letting, or to be let).
         This form of expression conforms to the use of the
         Anglo-Saxon gerund with to (dative infinitive) which
         was commonly so employed. See Gerund, 2. " Your
         elegant house in Harley Street is to let." --Thackeray.
         In the imperative mood, before the first person plural,
         let has a hortative force. " Rise up, let us go."
         --Mark xiv. 42. " Let us seek out some desolate shade."
         --Shak.
         [1913 Webster]

   To let alone, to leave; to withdraw from; to refrain from
      interfering with.

   To let blood, to cause blood to flow; to bleed.

   To let down.
      (a) To lower.
      (b) To soften in tempering; as, to let down tools,
          cutlery, and the like.

   To let fly or To let drive, to discharge with violence,
      as a blow, an arrow, or stone. See under Drive, and
      Fly.

   To let in or To let into.
      (a) To permit or suffer to enter; to admit.
      (b) To insert, or imbed, as a piece of wood, in a recess
          formed in a surface for the purpose.

   To let loose, to remove restraint from; to permit to wander
      at large.

   To let off.
      (a) To discharge; to let fly, as an arrow; to fire the
          charge of, as a gun.
      (b) To release, as from an engagement or obligation.
          [Colloq.]

   To let out.
      (a) To allow to go forth; as, to let out a prisoner.
      (b) To extend or loosen, as the folds of a garment; to
          enlarge; to suffer to run out, as a cord.
      (c) To lease; to give out for performance by contract, as
          a job.
      (d) To divulge.

   To let slide, to let go; to cease to care for. [Colloq.] "
      Let the world slide." --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Let \Let\, v. i.
   1. To forbear. [Obs.] --Bacon.
      [1913 Webster]

   2. To be let or leased; as, the farm lets for $500 a year.
      See note under Let, v. t.
      [1913 Webster]

   To let on, to tell; to tattle; to divulge something. [Low]


   To let up, to become less severe; to diminish; to cease;
      as, when the storm lets up. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

LET
    n 1: a brutal terrorist group active in Kashmir; fights against
         India with the goal of restoring Islamic rule of India;
         "Lashkar-e-Toiba has committed mass murders of civilian
         Hindus" [syn: Lashkar-e-Taiba, Lashkar-e-Toiba,
         Lashkar-e-Tayyiba, LET, Army of the Pure, Army of
         the Righteous]
    2: a serve that strikes the net before falling into the
       receiver's court; the ball must be served again [syn: let,
       net ball]
    v 1: make it possible through a specific action or lack of
         action for something to happen; "This permits the water to
         rush in"; "This sealed door won't allow the water come into
         the basement"; "This will permit the rain to run off" [syn:
         let, allow, permit] [ant: keep, prevent]
    2: actively cause something to happen; "I let it be known that I
       was not interested"
    3: consent to, give permission; "She permitted her son to visit
       her estranged husband"; "I won't let the police search her
       basement"; "I cannot allow you to see your exam" [syn:
       permit, allow, let, countenance] [ant: disallow,
       forbid, interdict, nix, prohibit, proscribe,
       veto]
    4: cause to move; cause to be in a certain position or
       condition; "He got his squad on the ball"; "This let me in
       for a big surprise"; "He got a girl into trouble" [syn:
       get, let, have]
    5: leave unchanged; "let it be"
    6: grant use or occupation of under a term of contract; "I am
       leasing my country estate to some foreigners" [syn: lease,
       let, rent]

Moby Thesaurus II by Grady Ward, 1.0:

161 Moby Thesaurus words for "let":
   OK, accord, accredit, admit, allow, approve, arrest, arrestation,
   arrestment, assume, authorize, bareboat charter, be afraid,
   believe, bleed, blockage, blocking, broach, certify, charter,
   chartered, check, clogging, closing up, closure, commission,
   concede, conceive, conclude, consent, consider, constriction,
   cramp, daresay, decant, deduce, deem, delay, detainment, detention,
   dispense, divine, draft, draft off, drain, draw, draw from,
   draw off, dream, employed, empty, endorse, exhaust, expect, fancy,
   farm, farm out, feel, fixation, foot-dragging, gather, give leave,
   give permission, give the go-ahead, give the word, grant,
   hampering, have, hindering, hindrance, hire, hire out, hired,
   hireling, hiring, holdback, holdup, imagine, impediment, infer,
   inhibition, interference, interruption, job, lease, lease out,
   lease-back, lease-lend, leased, leave, lend-lease, let be,
   let blood, let off, let out, license, make possible, mercenary,
   milk, negativism, nuisance value, obstruction, obstructionism,
   occlusion, okay, opine, opposition, paid, permit, phlebotomize,
   pipette, prefigure, presume, presuppose, presurmise,
   provisionally accept, pump, pump out, reckon, release, rent,
   rent out, rental, rented, repression, repute, resistance,
   restraint, restriction, retardation, retardment, sanction, say,
   say the word, setback, siphon off, squeeze, stranglehold,
   stricture, sublease, subleased, sublet, subrent, suck, suck out,
   suffer, suppose, suppression, surmise, suspect, take, take for,
   take for granted, take it, take to be, tap, think, underlet,
   understand, venesect, vouchsafe



Bouvier's Law Dictionary, Revised 6th Ed (1856):

LET. Hindrance, obstacle, obstruction; as, without let, molestation or
hindrance.