What is "trochoid"

Trochoid \Tro"choid\, n. [Gr. ? a wheel + -oid; cf. F. trocho["i]de. See Troche.] (Geom.) The curve described by any point in a wheel rolling on a line; a cycloid; a roulette; in general, the curve described by any point fixedly connected with a moving curve while the moving curve rolls without slipping on a second fixed curve, the curves all being in one plane. Cycloids, epicycloids, hypocycloids, cardioids, etc., are all trochoids.

Trochoid \Tro"choid\, a.

1. (Anat.) Admitting of rotation on an axis; -- sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column.

2. (Zo["o]l.) Top-shaped; having a flat base and conical spire; -- said of certain shells.

3. (Zo["o]l.) Of or pertaining to the genus Trochus or family Trochid[ae].

a. 1 capable of rolling 2 allowing rotation n. (context mathematics English) The curve traced by a point on a circle as it rolls along a straight line

thumb|290px|right|A cycloid (a common trochoid) generated by a rolling circle

A trochoid (from the Greek word for wheel, "trochos") is the curve described by a fixed point on a circle as it rolls along a straight line. The cycloid is a notable member of the trochoid family. The word "trochoid" was coined by Gilles de Roberval.