The Collaborative International Dictionary of English v.0.48:

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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