noun the constellation sextans.
2. sextant ·noun the sixth part of a circle.
3. sextant ·noun an instrument for measuring angular distances between objects, used ·esp. at sea, for ascertaining the latitude and longitude. it is constructed on the same optical principle as hadley's quadrant, but usually of metal, with a nicer graduation, telescopic sight, and its arc the sixth, and sometimes the third, part of a circle. ·see quadrant.