A person, group, thing, or course of action that is powerful, influential, or particularly effective.
A large artillery gun or one of the largest-caliber naval guns (as on a battleship).
A person, principle, or thing which acts as a guide; a guiding light; also, something which attracts much attention; a centre of attention.
The star visible to the naked eye which was in the past, is now, or will be in the future nearest a celestial pole of a planet.