Definition of: trochoid

(trō′koid) adjective
Rotating upon its own axis; pivotal: also tro·choi′dal.
—noun Math. A plane curve traced by a point on a circle or on its extended radius as the circle rolls, without slipping, on a straight line: when the point is on the circumference of the circle, the curve traced is a cycloid. [<Gk. trochoeidēs round, wheel–like <trochos a wheel + eidos form, shape]
—tro·choi′·dal·ly adverb