Epicycle
/ˈɛpɪsaɪkəl/noun
A small circle whose centre travels along a larger one, used in early astronomy to model planetary motion.
The Greek roots
Literally: “circle upon a circle”
The story of the word
A circle riding on a circle. Greek astronomers used the device to explain why planets sometimes appear to stop and reverse against the stars, and Ptolemy's version predicted positions well enough to stay in service for fourteen centuries. Chaucer already had the word in English in the 1390s. Its modern career as a byword for patching up a failing theory is unfair to the mathematics and fair enough to what came after it.
- How it travelled
- Ancient Greek → Latin → Old French → English
- First recorded
- late 14th century
The same roots elsewhere
Other languages reached for exactly the same Greek pieces.
Same family
In a sentence
Every fix they proposed was another epicycle bolted onto a model nobody believed.
Retrograde motion falls out of the epicycle without any need for the Earth to move.