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The Collaborative International Dictionary
Epicycloidal

Epicycloidal \Ep`i*cy*cloid"al\, a. Pertaining to the epicycloid, or having its properties.

Epicycloidal wheel, a device for producing straight-line motion from circular motion, on the principle that a pin fastened in the periphery of a gear wheel will describe a straight line when the wheel rolls around inside a fixed internal gear of twice its diameter.

Wiktionary
epicycloidal

a. Of or pertaining to an epicycloid.