The Collaborative International Dictionary of English v.0.48:

Gear \Gear\ (g[=e]r), n. [OE. gere, ger, AS. gearwe clothing,
   adornment, armor, fr. gearo, gearu, ready, yare; akin to OHG.
   garaw[imac], garw[imac] ornament, dress. See Yare, and cf.
   Garb dress.]
   1. Clothing; garments; ornaments.
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            Array thyself in thy most gorgeous gear. --Spenser.
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   2. Goods; property; household stuff. --Chaucer.
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            Homely gear and common ware.          --Robynson
                                                  (More's
                                                  Utopia).
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   3. Whatever is prepared for use or wear; manufactured stuff
      or material.
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            Clad in a vesture of unknown gear.    --Spenser.
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   4. The harness of horses or cattle; trapping.
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   5. Warlike accouterments. [Scot.] --Jamieson.
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   6. Manner; custom; behavior. [Obs.] --Chaucer.
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   7. Business matters; affairs; concern. [Obs.]
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            Thus go they both together to their gear. --Spenser.
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   8. (Mech.)
      (a) A toothed wheel, or cogwheel; as, a spur gear, or a
          bevel gear; also, toothed wheels, collectively.
      (b) An apparatus for performing a special function;
          gearing; as, the feed gear of a lathe.
      (c) Engagement of parts with each other; as, in gear; out
          of gear.
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   9. pl. (Naut.) See 1st Jeer
      (b) .
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   10. Anything worthless; stuff; nonsense; rubbish. [Obs. or
       Prov. Eng.] --Wright.
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             That servant of his that confessed and uttered this
             gear was an honest man.              --Latimer.
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   Bever gear. See Bevel gear.

   Core gear, a mortise gear, or its skeleton. See Mortise
      wheel, under Mortise.

   Expansion gear (Steam Engine), the arrangement of parts for
      cutting off steam at a certain part of the stroke, so as
      to leave it to act upon the piston expansively; the
      cut-off. See under Expansion.

   Feed gear. See Feed motion, under Feed, n.

   Gear cutter, a machine or tool for forming the teeth of
      gear wheels by cutting.

   Gear wheel, any cogwheel.

   Running gear. See under Running.

   To throw in gear or To throw out of gear (Mach.), to
      connect or disconnect (wheelwork or couplings, etc.); to
      put in, or out of, working relation.
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WordNet (r) 3.0 (2006):

gear wheel
    n 1: a toothed wheel that engages another toothed mechanism in
         order to change the speed or direction of transmitted
         motion [syn: gear, gear wheel, geared wheel,
         cogwheel]