## epicycloid

[ep′ə sī**′**klo̵id′]

noun

Geom. the curve traced by a point on the circumference of an epicycle that rolls around the outside of a fixed circle

Origin of epicycloid

epicycl(e) + -oid*Related Forms:*

- epicycloidal
adjective

## epicycloid

noun

The curve described by a point on the circumference of a circle as the circle rolls on the outside of the circumference of a second, fixed circle.

*Related Forms:*

**ep′i·cy·cloid′al**adjective

**epicycloid**

The parametric equations of an epicycloid are

x = (a + b) cos &thgr; - b cos (a + bb

&thgr;)

y = (a + b) sin &thgr; - b sin (a + bb

&thgr;).