Pronunciation: (trō'koid), [key]
Geom.a curve traced by a point on a radius or an extension of the radius of a circle that rolls, without slipping, on a curve, another circle, or a straight line. Equation: x = aθ - b sin θ, y = a - b cos θ.
rotating on an axis, as a wheel.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.