Epicycle
/ˈɛpɪˌsaɪkəl/noun
A small circle whose center moves around the circumference of a larger circle, formerly used to model planetary motion.
Did you know?In Ptolemaic astronomy, epicycles were used to explain why planets sometimes appear to reverse direction across the night sky, a phenomenon called retrograde motion.
Etymological Timeline
Proto-Indo-European
PIE
*kwel-
“To turn, revolve, or move around”
Ancient Greek
Greek
kýklos
“Circle, wheel, or circular movement”
Ancient Greek
Greek
epíkyklos
“A circle upon or around another circle”
Late Antiquity
Latin
epicyclus
“A small astronomical circle used in planetary models”
14th Century
Middle English
epicycle
“A circular orbit or circle used in astronomy”
Modern English
English
epicycle
“A small orbital circle used historically to represent planetary motion”