The Collaborative International Dictionary of English v.0.48:

Rack \Rack\, n. [Probably fr. D. rek, rekbank, a rack, rekken to
   stretch; akin to G. reck, reckbank, a rack, recken to
   stretch, Dan. r[ae]kke, Sw. r[aum]cka, Icel. rekja to spread
   out, Goth. refrakjan to stretch out; cf. L. porrigere, Gr.
   'ore`gein. [root]115. Cf. Right, a., Ratch.]
   1. An instrument or frame used for stretching, extending,
      retaining, or displaying, something. Specifically:
      (a) An engine of torture, consisting of a large frame,
          upon which the body was gradually stretched until,
          sometimes, the joints were dislocated; -- formerly
          used judicially for extorting confessions from
          criminals or suspected persons.
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                During the troubles of the fifteenth century, a
                rack was introduced into the Tower, and was
                occasionally used under the plea of political
                necessity.                        --Macaulay.
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      (b) An instrument for bending a bow.
      (c) A grate on which bacon is laid.
      (d) A frame or device of various construction for holding,
          and preventing the waste of, hay, grain, etc.,
          supplied to beasts.
      (e) A frame on which articles are deposited for keeping or
          arranged for display; as, a clothes rack; a bottle
          rack, etc.
      (f) (Naut.) A piece or frame of wood, having several
          sheaves, through which the running rigging passes; --
          called also rack block. Also, a frame to hold shot.
      (g) (Mining) A frame or table on which ores are separated
          or washed.
      (h) A frame fitted to a wagon for carrying hay, straw, or
          grain on the stalk, or other bulky loads.
      (i) A distaff.
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   2. (Mech.) A bar with teeth on its face, or edge, to work
      with those of a wheel, pinion, or worm, which is to drive
      it or be driven by it.
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   3. That which is extorted; exaction. [Obs.] --Sir E. Sandys.
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   Mangle rack. (Mach.) See under Mangle. n.

   Rack block. (Naut.) See def. 1
      (f), above.

   Rack lashing, a lashing or binding where the rope is
      tightened, and held tight by the use of a small stick of
      wood twisted around.

   Rack rail (Railroads), a toothed rack, laid as a rail, to
      afford a hold for teeth on the driving wheel of a
      locomotive for climbing steep gradients, as in ascending a
      mountain.

   Rack saw, a saw having wide teeth.

   Rack stick, the stick used in a rack lashing.

   To be on the rack, to suffer torture, physical or mental.


   To live at rack and manger, to live on the best at
      another's expense. [Colloq.]

   To put to the rack, to subject to torture; to torment.
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            A fit of the stone puts a king to the rack, and
            makes him as miserable as it does the meanest
            subject.                              --Sir W.
                                                  Temple.
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