Sextant

Part of speech: noun (n.)

1. The sixth part of a circle.

2. 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.

3. The constellation Sextans. Box sextant, a small sextant inclosed in a cylindrical case to make it more portable.