·adj Of or pertaining to the genus Trochus or family Trochidae.
II. Trochoid ·adj Top-shaped; having a flat base and conical spire;
— said of certain shells.
III. Trochoid ·adj Admitting of rotation on an axis;
— sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column.
IV. Trochoid ·noun 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.