Definition of "epicycle" [ep•i•cy•cle]

• In Ptolemaic cosmology, a small circle, the center of which moves on the circumference of a larger circle at whose center is the earth and the circumference of which describes the orbit of one of the planets around the earth. (noun)
• Mathematics A circle whose circumference rolls along the circumference of a fixed circle, thereby generating an epicycloid or a hypocycloid. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "For the epicycle is a sphere which changes place in the circumference of the large sphere."
• "Zizka makes an interesting point, I think, with his "epicycle" comment, but I don't believe that the rules that cover exceptions are necessarily made up."
• "I was thinking primarily of the "epicycle" business in Greek astronomy, where when the observations didn't match the theory, the theory wasn't reconsidered, additional elements were just bolted on for support."