Definition of: epicycle

(ep′ə·sī′kəl) noun
1. In the Ptolemaic cosmogony, a small circle whose center moves on the circumference of a larger circle (the deferent) concentric with the earth, while its own circumference forms the orbit of a planet.
2. Geom. A circle that rolls upon the exterior or interior of the circumference of another circle. [<L epicyclus <Gk. epikyklos <epi- upon + kyklos a circle]
—ep′i·cy′clic (-sī′klik, -sik′lik), ep′i·cy′cli·cal adjective
EPICYCLE
c. Earth.
e. Epicycle.
d.d.d. Deferent.
p. Planet.