deferent
The term "deferent" refers to a concept in astronomy, particularly in the context of the Ptolemaic system. In this geocentric model, the deferent is the large circle around the Earth on which a celestial body, such as a planet, moves. The deferent helps explain the apparent retrograde motion of planets by allowing them to move in a circular path while also accounting for their smaller circular movements, known as epicycles.
In modern terms, the concept of a deferent is less relevant due to the acceptance of the heliocentric model, where planets orbit the Sun. However, understanding deferents is important for grasping the historical development of astronomical theories and how ancient astronomers attempted to explain the movements of celestial bodies.