ETYM Cyclo- + -oid: cf. French cycloďde.
In geometry, a curve resembling a series of arches traced out by a point on the circumference of a circle that rolls along a straight line. Its applications include the study of the motion of wheeled vehicles along roads and tracks.
A line generated by a point on a circle rolling along a straight line.

Resembling a circle; SYN. cycloidal.