trochoid

Tro"choid, n. Etym: [Gr. -oid; cf. F. trochoïde. See Troche.] (Geom.) Defn: 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. Tro"choid, a. 1. (Anat.) Defn: Admitting of rotation on an axis; -- sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column. 2. (Zoöl.) Defn: Top-shaped; having a flat base and conical spire; -- said of certain shells. 3. (Zoöl.) Defn: Of or pertaining to the genus Trochus or family Trochidæ.

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