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 ]

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 ]

n. The quality or states of being spiral. [ 1913 Webster ]

adv. In a spiral form, manner, or direction. [ 1913 Webster ]

n. [ Spiral + zooid. So called because they often have a spiral form when contracted. ] (Zool.) One of the special defensive zooids of certain hydroids. They have the form of long, slender tentacles, and bear lasso cells. [ 1913 Webster ]