epicycle

n. [ L. epicyclus, Gr. &unr_;; 'epi` upon + &unr_; circle. See Cycle. ] 1. (Ptolemaic Astron.) A circle, whose center moves round in the circumference of a greater circle; or a small circle, whose center, being fixed in the deferent of a planet, is carried along with the deferent, and yet, by its own peculiar motion, carries the body of the planet fastened to it round its proper center. [ 1913 Webster ]

The schoolmen were like astronomers which did feign eccentrics, and epicycles, and such engines of orbs. Bacon. [ 1913 Webster ]

2. (Mech.) A circle which rolls on the circumference of another circle, either externally or internally. [ 1913 Webster ]