Ĕp'/i-cy'cloid, n.

noun

n. [Fr. épicycloïde, from Gr. ἐπί-κύκλος and εἶδος, form. See supra.] (Geom.) A curve generated by a point in the circumference of a movable circle, which rolls on the inside or outside of the circumference of a fixed circle, as by the point a or a' in the circle A or A'.

When the generating point is not in the circumference of the moving circle, the

A diagram of an epicycloid formed by a small circle rolling around a larger circle, with curves labeled a, A, A′, and a′. — Epicycloid.