What is the meaning of Epicycle?

A small circle whose centre is on the circumference of a larger circle; in Ptolemaic astronomy it was seen as the basis of revolution of the "seven planets", given a fixed central Earth.

Any circle whose circumference rolls around that of another circle, thus creating a hypocycloid or epicycloid.

A ring of atoms joining parts of an already cyclic compound

An ad hoc complication added to a model to make it fit the known data

Source: wiktionary.org