The Collaborative International Dictionary of English v.0.48:

Writhe \Writhe\, v. i.
   To twist or contort the body; to be distorted; as, to writhe
   with agony. Also used figuratively.
   [1913 Webster]

         After every attempt, he felt that he had failed, and
         writhed with shame and vexation.         --Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Writhe \Writhe\, v. t. [imp. Writhed; p. p. Writhed, Obs. or
   Poetic Writhen; p. pr. & vb. n. Writhing.] [OE. writhen,
   AS. wr[imac]?an to twist; akin to OHG. r[imac]dan, Icel.
   r[imac]?a, Sw. vrida, Dan. vride. Cf. Wreathe, Wrest,
   Wroth.]
   [1913 Webster]
   1. To twist; to turn; now, usually, to twist or turn so as to
      distort; to wring. "With writhing [turning] of a pin."
      --Chaucer.
      [1913 Webster]

            Then Satan first knew pain,
            And writhed him to and fro.           --Milton.
      [1913 Webster]

            Her mouth she writhed, her forehead taught to frown.
                                                  --Dryden.
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            His battle-writhen arms, and mighty hands.
                                                  --Tennyson.
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   2. To wrest; to distort; to pervert.
      [1913 Webster]

            The reason which he yieldeth showeth the least part
            of his meaning to be that whereunto his words are
            writhed.                              --Hooker.
      [1913 Webster]

   3. To extort; to wring; to wrest. [R.]
      [1913 Webster]

            The nobility hesitated not to follow the example of
            their sovereign in writhing money from them by every
            species of oppression.                --Sir W.
                                                  Scott.
      [1913 Webster]

WordNet (r) 3.0 (2006):

writhe
    v 1: to move in a twisting or contorted motion, (especially when
         struggling); "The prisoner writhed in discomfort"; "The
         child tried to wriggle free from his aunt's embrace" [syn:
         writhe, wrestle, wriggle, worm, squirm, twist]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "writhe":
   ache, agonize, ail, anguish, bend, blanch, bleed, blench, buckle,
   contort, crook, crumple, distort, feel pain, feel the pangs,
   fidget, flinch, flip out, flutter, freak out on, get high on, glow,
   gnarl, go hard with, go pitapat, grimace, have a misery,
   have the fidgets, have the shakes, heave, hurt, jerk, knot,
   palpitate, pant, pound, quake, quaver, quiver, recoil, screw,
   shake, shiver, shoot, shrink, smart, spring, squiggle, squirm,
   suffer, suffer anguish, swell, swell with emotion, thrash, thrill,
   thrill to, throb, tingle, tingle with excitement, toss,
   toss and turn, tremble, tumble, turn, turn awry, turn on to,
   twinge, twist, twist and turn, twitch, twitter, wag, waggle, warp,
   wiggle, wince, worm, wrench, wrest, wriggle, wring