Epicyclic

Part of speech: adjective

Definitions

1. Relating to a gear system where one circular element orbits a larger counterpart while also rotating independently on its axis
2. A mechanical system involving circular gears, where smaller ones rotate about larger gears, combining movement in a complex manner
3. Pertaining to a gearing arrangement that features smaller circles revolving around a larger center while turning on their own axes

Etymology: The word "epicyclic" is built from "epicycle" plus the adjective-forming suffix "-ic", so its history is essentially the history of its root. "Epicycle" comes from Greek "epikyklos", meaning "on a circle" or "upon a circle", combining "epi" (upon) with "kyklos" (circle, wheel). In ancient astronomy, an epicycle was a small circle whose centre travels around a larger circle, and Ptolemaic astronomers used this device to explain the apparently irregular paths of the planets across the sky. The suffix traces back much further. Its ultimate ancestry runs through Proto-Indo-European and Proto-Italic forms, passing into Latin as "-icus", then through Old French "-ique" and Middle English "-ik" before taking the modern English "-ic" form. The same suffix turns many English nouns into adjectives, such as "electric" or "epic". The modern sense is mechanical rather than astronomical. Epicyclic gear trains, in which smaller gears revolve around a central gear, reproduce the same geometry that ancient astronomers imagined for the heavens, so the word has moved from the sky into the workshop.