Pronunciation: (ep'u-sī"kul), [key]
1. Astron.a small circle the center of which moves around in the circumference of a larger circle: used in Ptolemaic astronomy to account for observed periodic irregularities in planetary motions.
2. Math.a circle that rolls, externally or internally, without slipping, on another circle, generating an epicycloid or hypocycloid.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.