The Collaborative International Dictionary of English v.0.48:

Spur \Spur\, n. [OE. spure, spore, AS. spura, spora; akin to D.
   spoor, G. sporn, OHG. sporo, Icel. spori, Dan. spore, Sw.
   sporre, and to AS. spor a trace, footstep, spyrian to trace,
   track, examine, and E. spurn. [root]171. Cf. Sparrow,
   Spere, Spoor, Spurn.]
   1. An implement secured to the heel, or above the heel, of a
      horseman, to urge the horse by its pressure. Modern spurs
      have a small wheel, or rowel, with short points. Spurs
      were the badge of knighthood.
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            And on her feet a pair of spurs large. --Chaucer.
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   2. That which goads to action; an incitement.
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            Fame is the spur that the clear spirit doth raise
            (That last infirmity of noble mind)
            To scorn delights and live laborious days. --Milton.
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   3. Something that projects; a snag.
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   4. One of the large or principal roots of a tree. --Shak.
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   5. (Zool.) Any stiff, sharp spine, as on the wings and legs
      of certain birds, on the legs of insects, etc.;
      especially, the spine on a cock's leg.
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   6. A mountain that shoots from any other mountain, or range
      of mountains, and extends to some distance in a lateral
      direction, or at right angles.
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   7. A spiked iron worn by seamen upon the bottom of the boot,
      to enable them to stand upon the carcass of a whale, to
      strip off the blubber.
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   8. (Carp.) A brace strengthening a post and some connected
      part, as a rafter or crossbeam; a strut.
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   9. (Arch.)
      (a) The short wooden buttress of a post.
      (b) A projection from the round base of a column,
          occupying the angle of a square plinth upon which the
          base rests, or bringing the bottom bed of the base to
          a nearly square form. It is generally carved in
          leafage.
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   10. (Bot.)
       (a) Any projecting appendage of a flower looking like a
           spur. --Gray.
       (b) Ergotized rye or other grain. [R.]
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   11. (Fort.) A wall that crosses a part of a rampart and joins
       to an inner wall.
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   12. (Shipbuilding)
       (a) A piece of timber fixed on the bilge ways before
           launching, having the upper ends bolted to the
           vessel's side.
       (b) A curved piece of timber serving as a half beam to
           support the deck where a whole beam can not be
           placed.
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   13. (Mining) A branch of a vein.
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   14. The track of an animal, as an otter; a spoor.
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   Spur fowl (Zool.), any one of several species of Asiatic
      gallinaceous birds of the genus Galloperdix, allied to
      the jungle fowl. The males have two or more spurs on each
      leg.

   Spur gear (Mach.), a cogwheel having teeth which project
      radially and stand parallel to the axis; a spur wheel.

   Spur gearing, gearing in which spur gears are used. See
      under Gearing.

   Spur pepper. (Bot.) See the Note under Capsicum.

   Spur wheel. Same as Spur gear, above.
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WordNet (r) 3.0 (2006):

spur gear
    n 1: gear wheels that mesh in the same plane [syn: spur gear,
         spur wheel]