Real Dictionary

spiral
countable noun: A spiral is a shape which winds round and round, with each curve above or outside the previous one.

spiral in American English
a spiral curve occurring in a single plane
circling around a central point in a flat, two-dimensional curve that constantly increases (or decreases) in size
adjective: running continuously around a fixed point or center while constantly receding from or approaching it; coiling in a single plane
intransitive verb: to take a spiral form or course
noun: a plane curve generated by a point moving around a fixed point while constantly receding from or approaching it
transitive verb: to cause to take a spiral form or course

spiral in British English
adjective: having the shape of a spiral
noun: one of several plane curves formed by a point winding about a fixed point at an ever-increasing distance from it. Polar equation of Archimedes spiral: r = aθ; of logarithmic spiral: log r = aθ; of hyperbolic spiral: rθ = a, (where a is a constant)
verb: to assume or cause to assume a spiral course or shape