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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