epicycle
UK[ˈepɪˌsaɪkəl]US[ˈepəˌsaɪkəl]
n
a small circle whose center moves around the circumference of a larger one, used in ptolemaic astronomy to explain observed planetary motions.
n
a circle rolling on the outside or inside of another circle, generating an epicycloid or hypocycloid.
Morpheme Breakdown
epi
cycle
epi
upon
cycle
circle
Etymology
the term 'epicycle' is a direct borrowing from late latin 'epicyclus', which itself originates from greek 'epikyklos', meaning 'moving on a circle'. it is a compound of the prefix 'epi-' (upon) and 'kyklos' (circle). in ancient greek astronomy, this term was used to describe a conceptual model where a planet moved in a small circle, the center of which itself moved along a larger circular orbit around the earth. this elegant, though ultimately incorrect, geometrical construction was central to the ptolemaic system, aiming to reconcile the observed retrograde motion of planets with the philosophical ideal of uniform circular motion.
Analysis
Structure: epi (upon) + cycle (circle)
epi is a prefix of greek origin meaning 'upon', 'at', or 'beside'. cycle is a root of greek origin (kyklos) meaning 'circle' or 'wheel'.
Examples
in the ptolemaic model, the complex path of mars was explained using an epicycle.
the mathematician demonstrated how an epicycle rolling on the outside of a fixed circle generates an epicycloid curve.
the introduction of the epicycle was a clever attempt to save the phenomena of planetary motion within a geocentric framework.