n. [ Gr. &unr_; 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. [ 1913 Webster ]

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. [ 1913 Webster ]

2. (Zool.) Top-shaped; having a flat base and conical spire; -- said of certain shells. [ 1913 Webster ]

3. (Zool.) Of or pertaining to the genus Trochus or family Trochidae. [ 1913 Webster ]

a. 1. (Geom.) Of or pertaining to a trochoid; having the properties of a trochoid. [ 1913 Webster ]

2. (Anat. & Zool.) See Trochoid, a. [ 1913 Webster ]