Definition of epicycle in English:



  • 1Geometry
    A small circle whose centre moves round the circumference of a larger one.

    • ‘The historically older concept of epicycles (small cycles on a bigger cycle) has not found use in the geological literature.’
    • ‘Other threads appeared out of nowhere, forming, with epicycles and Celtic knotting, a mesh bag that pulled him irresistibly toward the bleak globe that was the Inquisitor.’
    • ‘Waves come in like epicycles rippling through the larger cycles of tides, and the moon's revolution around the Earth, and the Earth's revolution around the sun.’
    1. 1.1historical An epicycle used to describe planetary orbits in the Ptolemaic system.
      • ‘A planet moves uniformly on a circle called an epicycle, and the epicycle in turn moves uniformly on a circle called the deferent.’
      • ‘For example, each planet was said to move in its own small curve called an epicycle, while all the epicycles moved around the earth in larger circles called deferents.’
      • ‘Although orbits were discussed by the Greeks they were attempting to derive orbits for the planets round the Earth so are of little interest to us in this article although the method of epicycles is an early application of Fourier series.’
      • ‘This is not strictly true since the theory of epicycles certainly predates Apollonius.’
      • ‘In the epicycle theory the Earth is in the centre of a circle which has smaller circles rotating round its circumference.’


Late Middle English from Old French, or via late Latin from Greek epikuklos, from epi ‘upon’ + kuklos ‘circle’.