noun
magnetic compass
A device that uses a magnetized needle to indicate direction; the standard term for a compass in navigation and science contexts.
方位磁石を使って北の方角を確認した。
I checked the direction of north using a magnetic compass.
コンパス is a more general loanword that can refer to a drawing compass or a magnetic compass, while 方位磁石 specifically means a magnetic compass.
Compound of 方位 (direction) and 磁石 (magnet), literally 'direction magnet'.