<p><strong>Noun</strong></p><ul><li>context: Astronomy</li><li>definition: a small circle the center of which moves around in the circumference of a larger circle; used in Ptolemaic astronomy to account for observed periodic irregularities in planetary motions</li><li>context: Mathematics</li><li>definition: a circle that rolls, externally or internally, without slipping, on another circle, generating an epicycloid or hypocycloid</li></ul>