The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. Anything which has a spiral form, as a spiral shell.
      [1913 Webster]

   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.
      [1913 Webster]

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.
      [1913 Webster]

   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.
      [1913 Webster]

   3. (Geom.) Of or pertaining to a spiral; like a spiral.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spiral
    adj 1: in the shape of a coil [syn: coiling, helical,
           spiral, spiraling, volute, voluted, whorled,
           turbinate]
    n 1: a plane curve traced by a point circling about the center
         but at increasing distances from the center
    2: a curve that lies on the surface of a cylinder or cone and
       cuts the element at a constant angle [syn: helix, spiral]
    3: a continuously accelerating change in the economy
    4: ornament consisting of a curve on a plane that winds around a
       center with an increasing distance from the center [syn:
       spiral, volute]
    5: a structure consisting of something wound in a continuous
       series of loops; "a coil of rope" [syn: coil, spiral,
       volute, whorl, helix]
    6: flying downward in a helical path with a large radius
    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, spiral, coil]
    2: form a spiral; "The path spirals up the mountain"
    3: move in a spiral or zigzag course [syn: corkscrew,
       spiral]

Moby Thesaurus II by Grady Ward, 1.0:

218 Moby Thesaurus words for "spiral":
   Milky Way, O-shaped, Via Lactea, acrobatics, aerobatics, ambagious,
   anfractuous, arise, ascend, aspire, backhanded, bank, banking,
   barred spiral, barred spiral galaxy, become airborne, chandelle,
   circle, circling, circuit, circuiteer, circuition, circuitous,
   circuitousness, circuitry, circular, circularity, circulate,
   circulation, circumambience, circumambiency, circumambulate,
   circumambulation, circumflexion, circumlocution, circummigrate,
   circummigration, circumnavigate, circumnavigation, circumvent,
   cirrus, claw skyward, close the circle, cochlear, cochleate, coil,
   coiled, come full circle, come up, compass, corkscrew, corkscrewy,
   cosmic noise, crab, crabbing, curl, curl upwards, curlicue, cycle,
   describe a circle, deviance, deviancy, deviating, deviation,
   deviative, devious, deviousness, digression, digressive, dip,
   discursive, dive, diving, encircle, encompass, entwine, evolute,
   excursion, excursive, excursus, feather, fishtail, fishtailing,
   flank, float, fly, fly aloft, gain altitude, galactic circle,
   galactic cluster, galactic coordinates, galactic latitude,
   galactic longitude, galactic nebula, galactic noise, galactic pole,
   galaxy, girdle, girdle the globe, glide, go about, go around,
   go round, go the round, go up, grow up, gyre, gyring, hang,
   helical, helicoid, helix, hover, indirect, indirection, involute,
   island universe, kink, kite, lap, leave the ground, levitate, loom,
   loop, make a circuit, meandering, mount, nose dive, oblique, orbit,
   orbital, orbiting, out-of-the-way, plane, plow, poise, porpoise,
   power dive, pull out, pull up, pull-up, pullout, push down,
   pushdown, rear, rear up, revolve, ringlet, rise, rise up, roll,
   rolling, rotary, round, roundabout, roundaboutness, rounding,
   screw, screw-shaped, scroll, scrolled, sideslip, skid, skirt, soar,
   spheroidal galaxy, spin, spiral galaxy, spiral nebula, spiraling,
   spire, spiroid, stall, stand up, stunt, stunting, supergalaxy,
   surge, surround, swarm up, sweep up, swirl, tactical maneuvers,
   take off, tendril, tower, turbinal, turbinate, turn, turning,
   twine, twirl, twist, undulate, up, upgo, upgrow, upheave, uprise,
   upspin, upstream, upsurge, upswarm, upwind, verticillate, volplane,
   volute, voluted, volution, vortex, wheel, wheeling, whirl, whorl,
   whorled, wreathe, yaw, zoom