a compass consisting of a motor-operated gyroscope whose rotating axis, kept in a horizontal plane, takes a position parallel to the axis of the earth's rotation and thus points to the geographical north pole instead of to the magnetic pole
See gyrocompass in American Heritage Dictionary 4
noun
A compass with a motorized gyroscope whose angular momentum interacts with the force produced by the earth's rotation to maintain a north-south orientation of the gyroscopic spin axis, thereby providing a stable directional reference.