epicycle

Meaning

Noun

• 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

Origin

• From Latin epicyclus, from Ancient Greek ἐπίκυκλος, from ἐπί + κύκλος.