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.-admitting of rotation on an axis; -- sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column.-top-shaped; having a flat base and conical spire; -- said of certain shells.-of or pertaining to the genus trochus or family trochidae.