Sextant \Sex"tant\, n. [L. sextans, -antis, the sixth part of an as, fr. sextus sixth, sex six. See Six.]

1. (Math.) 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. (Astron.) The constellation Sextans.

Box sextant, a small sextant inclosed in a cylindrical case to make it more portable.

Source: Webster's Revised Unabridged Dictionary (1913)