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.

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.

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.