Tro"choid (?), n. [Gr. &?; a wheel + - oid; cf. F. trochoïde. 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.

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. (Zoöl.) Top-shaped; having a flat base and conical spire; -- said of certain shells.

3. (Zoöl.) Of or pertaining to the genus Trochus or family Trochidæ.

Tro"choid (?), n. [Gr. &?; a wheel + - oid; cf. F. trochoïde. 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.

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. (Zoöl.) Top-shaped; having a flat base and conical spire; -- said of certain shells.

3. (Zoöl.) Of or pertaining to the genus Trochus or family Trochidæ.