gy·ro·com·pass 
(jīrō-kŭm′pəs, -kŏm′-)
(jīrō-kŭm′pəs, -kŏm′-)n.
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.