- noun a device consisting of a spinning wheel, mounted on a base so that its axis can turn freely in one or more directions and thereby maintain its own direction even when the base is moved
- A mechanical device consisting of a heavy spinning wheel mounted on a gimble. The spinning wheel maintains the same orientation in space, regardless of how the base is turned. When mounted on a double gimbal it is free to rotate in three mutually perpendicular axes. Used, for instance, in a gyrocompass. Its abbreviation is gyro.