The Collaborative International Dictionary of English v.0.48:

Hinge \Hinge\, n. [OE. henge, heeng; akin to D. heng, LG. henge,
   Prov. E. hingle a small hinge; connected with hang, v., and
   Icel. hengja to hang. See Hang.]
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   1. The hook with its eye, or the joint, on which a door,
      gate, lid, etc., turns or swings; a flexible piece, as a
      strip of leather, which serves as a joint to turn on.
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            The gate self-opened wide,
            On golden hinges turning.             --Milton.
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   2. That on which anything turns or depends; a governing
      principle; a cardinal point or rule; as, this argument was
      the hinge on which the question turned.
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   3. One of the four cardinal points, east, west, north, or
      south. [R.]
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            When the moon is in the hinge at East. --Creech.
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            Nor slept the winds . . . but rushed abroad.
                                                  --Milton.
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   Hinge joint.
      (a) (Anat.) See Ginglymus.
      (b) (Mech.) Any joint resembling a hinge, by which two
          pieces are connected so as to permit relative turning
          in one plane.

   To be off the hinges, to be in a state of disorder or
      irregularity; to have lost proper adjustment. --Tillotson.
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WordNet (r) 3.0 (2006):

hinge joint
    n 1: a freely moving joint in which the bones are so articulated
         as to allow extensive movement in one plane [syn: hinge
         joint, ginglymus, ginglymoid joint]
    2: a joint allowing movement in one plane only [syn: knuckle
       joint, hinge joint]