Emily Dickinson Lexicon

CY'CLOID, n. [Gr. κυκλος, circle, and ειδος, form.]

A geometrical curve on which depends the doctrine of pendulums; a figure made by the upper end of the diameter of a circle, turning about a right line. – Bailey. The genesis of a cycloid may be conceived by imagining a nail in the circumference of a wheel; the line which the nail describes in the air, while the wheel revolves in a right line, is the cycloid. – Johnson.