Source : Webster's Revised Unabridged Dictionary (1913)

Spiral \Spi"ral\, n. [Cf. F. spirale. See {Spiral}, a.]
   1. (Geom.) A plane curve, not re["e]ntrant, 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}.

   2. Anything which has a spiral form, as a spiral shell.

   {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.

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.

Source : WordNet®

spiral
     adj : in the shape of a coil [syn: {coiling}, {helical}, {spiraling},
            {volute}, {voluted}, {whorled}, {turbinate}]
     [also: {spiralling}, {spiralled}]

spiral
     n 1: a plane curve traced by a point circling about the center
          but at ever-greater distances from it
     2: a curve that lies on the surface of a cylinder or cone and
        cuts the element at a constant angle [syn: {helix}]
     3: ornament consisting of a curve on a plane that winds around
        a center with an increasing distance from the center [syn:
         {volute}]
     4: a structure consisting of something wound in a continuous
        series of loops; "a coil of rope" [syn: {coil}, {volute},
        {whorl}, {helix}]
     5: flying downward in a helical path with a large radius
     [also: {spiralling}, {spiralled}]

spiral
     v 1: to wind or move in a spiral course; "the muscles and nerves
          of his fine drawn body were coiling for action"; "black
          smoke coiling up into the sky"; "the young people
          gyrated on the dance floor" [syn: {gyrate}, {coil}]
     2: form a spiral; "The path spirals up the mountain"
     3: move in a spiral or zigzag course [syn: {corkscrew}]
     [also: {spiralling}, {spiralled}]