WordWeb Online

1. (anatomy) admitting of rotation on an axis; sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column
    
2. (of shells) having a flat base and conical spire

1. The curve described by any point in a wheel rolling on a line; a cycloid; 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

Derived forms: trochoids

Encyclopedia: Trochoid