n. A circle moving upon or around another circle, as one of a number of wheels revolving round a common axis. See epicyclic train, under epicyclic.n. In the Ptolemaic system of astronomy, a little circle, conceived for the explanation of planetary motion, whose center was supposed to move round in the circumference of a greater circle; a small circle whose center, being fixed in the deferent of a planet, was supposed to be carried along with the deferent, and yet by its own peculiar motion to carry the body of the planet fastened to it round its proper center. Copernicus also made use of epicycles, which, however, were banished by Kepler.n. In mod. astron., sometimes used for the geocentric path of a planet, or its path relative to the earth regarded as fixed.