The Collaborative International Dictionary
Equant \E"quant\, n. [L. aequans, -antis, p. pr. of aequare: cf. F. ['e]quant. See Equate.] (Ptolemaic Astron.) A circle around whose circumference a planet or the center of ann epicycle was conceived to move uniformly; -- called also eccentric equator.
Wiktionary
a. Having comparable measurements in all directions; equidimensional. n. (context obsolete astronomy English) The center of a planetary epicycle.
Wikipedia
Equant (or punctum aequans) is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of the planets. The equant is used to explain the observed speed change in planetary orbit during different stages of the orbit. This planetary concept allowed Ptolemy to keep the theory of uniform circular motion alive by stating that the path of heavenly bodies was uniform around one point and circular around another point.
Usage examples of "equant".
He wears the Aristotelian cosmology like a shackle, clings to it like a wet-nurse, feeds upon its milk of false assumptions, and postulates the most unlikely machinery of epicycle, deferent, and equant.
Hipparchus seems to have taken as his starting point a work on eccentrics and equants by the Greek geometer, Apollonius of Perga (c.