Spiral \Spi"ral\, n. [Cf. F. spirale. See {Spiral}, a.]
   1. (Geom.) A plane curve, not reentrant, described by a
      point, called the generatrix, moving along a straight line
      according to a mathematical law, while the line is
      revolving about a fixed point called the pole. Cf.
      {Helix}.
      
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   2. Anything which has a spiral form, as a spiral shell.
      
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   {Equiangular spiral},a plane curve which cuts all its
      generatrices at the same angle. Same as {Logarithmic  spiral}, under {Logarithmic}.

   {Spiral of Archimedes}, a spiral the law of which is that the
      generatrix moves uniformly along the revolving line, which
      also moves uniformly.
      
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Spiral \Spi"ral\, a. [Cf. F. spiral. See {Spire} a winding
   line.]
   1. Winding or circling round a center or pole and gradually
      receding from it; as, the spiral curve of a watch spring.
      
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   2. Winding round a cylinder or imaginary axis, and at the
      same time rising or advancing forward; winding like the
      thread of a screw; helical.
      
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   3. (Geom.) Of or pertaining to a spiral; like a spiral.
      
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   {Spiral gear}, or {Spiral wheel} (Mach.), a gear resembling
      in general a spur gear, but having its teeth cut at an
      angle with its axis, or so that they form small portions
      of screws or spirals.

   {Spiral gearing}, a kind of gearing sometimes used in light
      machinery, in which spiral gears, instead of bevel gears,
      are used to transmit motion between shafts that are not
      parallel.

   {Spiral operculum}, an operculum whih has spiral lines of
      growth.

   {Spiral shell}, any shell in which the whorls form a spiral
      or helix.

   {Spiral spring}. See the Note under {Spring}, n., 4.
      
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