sextant

1. (nautical) A navigational device for deriving angular distances between objects so as to determine latitude and longitude.Examples: "[…] I can do more with a Quadrant, Sextant or Octant, of 1 foot Radius, furniſhed with Teleſcopical Sights and Screws, then ^([sic]) can poſſibly be done with any other Inſtrument, furniſhed only with Common Sights, though 10, 20, 30, nay threeſcore foot Radius; […]"; "I took our position every morning with my crude sextant; but the results were always most unsatisfactory."; "Moskowitz and Devereux have designed a hyperaccurate sextant for interstellar navigation based upon the design of the sextant used by the Apollo astronauts."

2. (geometry) One sixth of a circle or disc; a sector with an angle of 60°.

3. (dentistry) One of six groups of adjacent teeth, excluding the wisdom teeth.

4. (botany) A radial cell division of segments in three series, a sixth part of the original.