The Collaborative International Dictionary of English v.0.48:

Buckle \Buc"kle\, v. t. [imp. & p. p. Buckled; p. pr. & vb. n.
   Buckling.] [OE. boclen, F. boucler. See Buckle, n.]
   1. To fasten or confine with a buckle or buckles; as, to
      buckle a harness.
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   2. To bend; to cause to kink, or to become distorted.
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   3. To prepare for action; to apply with vigor and
      earnestness; -- formerly, generally used reflexively, but
      by mid 20th century, usually used with down; -- as, the
      programmers buckled down and worked late hours to finish
      the project in time for the promised delivery date.
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            Cartwright buckled himself to the employment.
                                                  --Fuller.
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   4. To join in marriage. [Scot.] --Sir W. Scott.
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The Collaborative International Dictionary of English v.0.48:

Buckle \Buc"kle\, n. [OE. bocle buckle, boss of a shield, OF.
   bocle, F. boucle, boss of a shield, ring, fr. L. buccula a
   little cheek or mouth, dim. of bucca cheek; this boss or knob
   resembling a cheek.]
   1. A device, usually of metal, consisting of a frame with one
      more movable tongues or catches, used for fastening things
      together, as parts of dress or harness, by means of a
      strap passing through the frame and pierced by the tongue.
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   2. A distortion bulge, bend, or kink, as in a saw blade or a
      plate of sheet metal. --Knight.
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   3. A curl of hair, esp. a kind of crisp curl formerly worn;
      also, the state of being curled.
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            Earlocks in tight buckles on each side of a lantern
            face.                                 --W. Irving.
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            Lets his wig lie in buckle for a whole half year.
                                                  --Addison.
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   4. A contorted expression, as of the face. [R.]
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            'Gainst nature armed by gravity,
            His features too in buckle see.       --Churchill.
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The Collaborative International Dictionary of English v.0.48:

Buckle \Buc"kle\ (b[u^]k"k'l), v. i.
   1. To bend permanently; to become distorted; to bow; to curl;
      to kink.
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            Buckled with the heat of the fire like parchment.
                                                  --Pepys.
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   2. To bend out of a true vertical plane, as a wall.
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   3. To yield; to give way; to cease opposing. [Obs.]
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            The Dutch, as high as they seem, do begin to buckle.
                                                  --Pepys.
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   4. To enter upon some labor or contest; to join in close
      fight; to struggle; to contend.
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            The bishop was as able and ready to buckle with the
            Lord Protector as he was with him.    --Latimer.
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            In single combat thou shalt buckle with me. --Shak.
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   To buckle to, to bend to; to engage with zeal.
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            To make our sturdy humor buckle thereto. --Barrow.
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            Before buckling to my winter's work.  --J. D.
                                                  Forbes.
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WordNet (r) 3.0 (2006):

buckle
    n 1: fastener that fastens together two ends of a belt or strap;
         often has loose prong
    2: a shape distorted by twisting or folding [syn: warp,
       buckle]
    v 1: fasten with a buckle or buckles [syn: buckle, clasp]
         [ant: unbuckle]
    2: fold or collapse; "His knees buckled" [syn: buckle,
       crumple]
    3: bend out of shape, as under pressure or from heat; "The
       highway buckled during the heat wave" [syn: heave,
       buckle, warp]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "buckle":
   anamorphism, anamorphosis, articulate, asymmetry, batten,
   batten down, bend, bolt, bulge, butt, button, catch, cave in,
   clasp, cleat, clip, collapse, contort, contortion, crook,
   crookedness, crumple, detorsion, deviation, disproportion, distort,
   distortion, dovetail, fastener, fastening, gnarl, hasp, hinge,
   hitch, hook, imbalance, irregularity, jam, joint, knot, latch,
   lock, lopsidedness, miter, mortise, nail, peg, pin, quirk, rabbet,
   rivet, scarf, screw, sew, skewer, snap, spring, staple, stick,
   stitch, tack, toggle, torsion, tortuosity, turn, turn awry, twist,
   unsymmetry, warp, wedge, wrench, wrest, wring, writhe, zipper