The Collaborative International Dictionary of English v.0.48:

Wrench \Wrench\ (r[e^]nch), n. [OE. wrench deceit, AS. wrenc
   deceit, a twisting; akin to G. rank intrigue, crookedness,
   renken to bend, twist, and E. wring. [root]144. See Wring,
   and cf. Ranch, v. t.]
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   1. Trick; deceit; fraud; stratagem. [Obs.]
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            His wily wrenches thou ne mayst not flee. --Chaucer.
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   2. A violent twist, or a pull with twisting.
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            He wringeth them such a wrench.       --Skelton.
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            The injurious effect upon biographic literature of
            all such wrenches to the truth, is diffused
            everywhere.                           --De Quincey.
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   3. A sprain; an injury by twisting, as in a joint.
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   4. Means; contrivance. [Obs.] --Bacon.
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   5. An instrument, often a simple bar or lever with jaws or an
      angular orifice either at the end or between the ends, for
      exerting a twisting strain, as in turning bolts, nuts,
      screw taps, etc.; a screw key. Many wrenches have
      adjustable jaws for grasping nuts, etc., of different
      sizes.
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   6. (Mech.) The system made up of a force and a couple of
      forces in a plane perpendicular to that force. Any number
      of forces acting at any points upon a rigid body may be
      compounded so as to be equivalent to a wrench.
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   Carriage wrench, a wrench adapted for removing or
      tightening the nuts that confine the wheels on the axles,
      or for turning the other nuts or bolts of a carriage or
      wagon.

   Monkey wrench. See under Monkey.

   Wrench hammer, a wrench with the end shaped so as to admit
      of being used as a hammer.
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The Collaborative International Dictionary of English v.0.48:

Wrench \Wrench\, v. t. [imp. & p. p. Wrenched; p. pr. & vb. n.
   Wrenching.] [OE. wrenchen, AS. wrencan to deceive,
   properly, to twist, from wrenc guile, deceit, a twisting.
   ????. See Wrench, n.]
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   1. To pull with a twist; to wrest, twist, or force by
      violence.
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            Wrench his sword from him.            --Shak.
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            Forthwith this frame of mine was wrenched
            With a woeful agony.                  --Coleridge.
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   2. To strain; to sprain; hence, to distort; to pervert.
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            You wrenched your foot against a stone. --Swift.
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WordNet (r) 3.0 (2006):

wrench
    n 1: a sharp strain on muscles or ligaments; "the wrench to his
         knee occurred as he fell"; "he was sidelined with a
         hamstring pull" [syn: wrench, twist, pull]
    2: a jerky pulling movement [syn: twist, wrench]
    3: a hand tool that is used to hold or twist a nut or bolt [syn:
       wrench, spanner]
    v 1: twist or pull violently or suddenly, especially so as to
         remove (something) from that to which it is attached or
         from where it originates; "wrench a window off its hinges";
         "wrench oneself free from somebody's grip"; "a deep sigh
         was wrenched from his chest" [syn: wrench, twist]
    2: make a sudden twisting motion
    3: twist and compress, as if in pain or anguish; "Wring one's
       hand" [syn: wring, wrench]
    4: twist suddenly so as to sprain; "wrench one's ankle"; "The
       wrestler twisted his shoulder"; "the hikers sprained their
       ankles when they fell"; "I turned my ankle and couldn't walk
       for several days" [syn: twist, sprain, wrench, turn,
       wrick, rick]