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.]
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            He . . . prayed him his voyage for to let.
                                                  --Chaucer.
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            Yet neither spins nor cards, ne cares nor frets,
            But to her mother Nature all her care she lets.
                                                  --Spenser.
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            Let me alone in choosing of my wife.  --Chaucer.
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   2. To consider; to think; to esteem. [Obs.] --Chaucer.
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   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.]
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            This irous, cursed wretch
            Let this knight's son anon before him fetch.
                                                  --Chaucer.
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            He . . . thus let do slay hem all three. --Chaucer.
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            Anon he let two coffers make.         --Gower.
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   4. To permit; to allow; to suffer; -- either affirmatively,
      by positive act, or negatively, by neglecting to restrain
      or prevent.
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   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.
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               Pharaoh said, I will let you go.   --Ex. viii.
                                                  28.
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               If your name be Horatio, as I am let to know it
               is.                                --Shak.
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   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.
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   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.
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   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.
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   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.
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WordNet (r) 3.0 (2006):

letting
    n 1: property that is leased or rented out or let [syn: lease,
         rental, letting]