Source : Webster's Revised Unabridged Dictionary (1913)

Epicycle \Ep"i*cy`cle\, n. [L. epicyclus, Gr. ?; 'epi` upon + ?
   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.

            The schoolmen were like astronomers which did feign
            eccentries, and epicycles, and such engines of orbs.
                                                  --Bacon.

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

Source : WordNet®

epicycle
     n : a circle that rolls around (inside or outside) another
         circle; generates an epicycloid or hypocycloid