Spiral (?), 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]