The Collaborative International Dictionary of English v.0.48:

Shackle \Shac"kle\, v. t. [imp. & p. p. Shackled; p. pr. & vb.
   n. Shackling.]
   1. To tie or confine the limbs of, so as to prevent free
      motion; to bind with shackles; to fetter; to chain.
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            To lead him shackled, and exposed to scorn
            Of gathering crowds, the Britons' boasted chief.
                                                  --J. Philips.
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   2. Figuratively: To bind or confine so as to prevent or
      embarrass action; to impede; to cumber.
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            Shackled by her devotion to the king, she seldom
            could pursue that object.             --Walpole.
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   3. To join by a link or chain, as railroad cars. [U. S.]
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   Shackle bar, the coupling between a locomotive and its
      tender. [U.S.]

   Shackle bolt, a shackle. --Sir W. Scott.
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The Collaborative International Dictionary of English v.0.48:

Shackle \Shac"kle\, n.
   Stubble. [Prov. Eng.] --Pegge.
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The Collaborative International Dictionary of English v.0.48:

Shackle \Shac"kle\, n. [Generally used in the plural.] [OE.
   schakkyll, schakle, AS. scacul, sceacul, a shackle, fr.
   scacan to shake; cf. D. schakel a link of a chain, a mesh,
   Icel. sk["o]kull the pole of a cart. See Shake.]
   1. Something which confines the legs or arms so as to prevent
      their free motion; specifically, a ring or band inclosing
      the ankle or wrist, and fastened to a similar shackle on
      the other leg or arm, or to something else, by a chain or
      a strap; a gyve; a fetter.
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            His shackles empty left; himself escaped clean.
                                                  --Spenser.
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   2. Hence, that which checks or prevents free action.
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            His very will seems to be in bonds and shackles.
                                                  --South.
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   3. A fetterlike band worn as an ornament.
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            Most of the men and women . . . had all earrings
            made of gold, and gold shackles about their legs and
            arms.                                 --Dampier.
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   4. A link or loop, as in a chain, fitted with a movable bolt,
      so that the parts can be separated, or the loop removed; a
      clevis.
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   5. A link for connecting railroad cars; -- called also
      drawlink, draglink, etc.
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   6. The hinged and curved bar of a padlock, by which it is
      hung to the staple. --Knight.
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   Shackle joint (Anat.), a joint formed by a bony ring
      passing through a hole in a bone, as at the bases of
      spines in some fishes.
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WordNet (r) 3.0 (2006):

shackle
    n 1: a restraint that confines or restricts freedom (especially
         something used to tie down or restrain a prisoner) [syn:
         shackle, bond, hamper, trammel]
    2: a U-shaped bar; the open end can be passed through chain
       links and closed with a bar
    v 1: bind the arms of [syn: pinion, shackle]
    2: restrain with fetters [syn: fetter, shackle]

Moby Thesaurus II by Grady Ward, 1.0:

171 Moby Thesaurus words for "shackle":
   Oregon boat, anchor, arrest, bar, barrier, bearing rein, bilbo,
   bind, bit, bond, bonds, bottle up, box up, bracelets, brake,
   bridle, burden, cage, camisole, chain, chains, check, checkrein,
   chock, clog, cloister, collar, confine, constrain, control, coop,
   coop in, coop up, cork up, countercheck, cramp, crib, cripple,
   cuffs, cumber, curb, curb bit, damper, detain, deter, deterrent,
   discourage, doorstop, drag, drag sail, drift anchor, drift sail,
   drogue, embarrass, encage, enchain, enclose, encumber, encumbrance,
   enmesh, ensnarl, entangle, entoil, entrammel, entrap, entwine,
   fasten, fence in, fetter, fetters, gag, gyve, gyves, halter,
   hamper, hamstring, handcuff, handcuffs, handicap, hem in, hinder,
   hindrance, hobble, hobbles, hog-tie, hold, hold back,
   hold in custody, hold in restraint, holdback, hopple, hopples,
   immure, impede, impediment, impound, inhibit, involve, irons,
   keep in, keep in custody, keep in detention, lame, lash,
   leading strings, leash, lime, limit, lumber, make fast, manacle,
   martingale, mew, mew up, moor, muzzle, net, obstacle, obstruction,
   peg down, pelham, pen, pen up, picket, pillory, pin down, pinion,
   pound, press down, put in irons, rail in, rein, reins, remora,
   restrain, restraint, restraints, restrict, restriction, rope,
   saddle with, scotch, sea anchor, seal up, secure, shackles,
   shut in, shut up, snaffle, snarl, spoke, stay, stocks, stop,
   straightjacket, strait-waistcoat, straitjacket, stranglehold,
   strap, tangle, tether, tie, tie down, tie up, toil, trammel,
   trammels, truss, wall in, weigh down, yoke