Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

   3. (Geom.) Of or pertaining to a spiral; like a spiral.

   {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.