sex·tant 
(sĕkstənt)
(sĕkstənt)n.
1. A navigational instrument containing a graduated 60-degree arc, used for measuring the altitudes of celestial bodies for use in determining the latitude and longitude of the observer.
2. Sextant See Sextans.
[New Latin sextāns, sextant-, from Latin, sixth part (so called because the instrument's arc is a sixth of a circle), from sextus, sixth; see s(w)eks in the Appendix of Indo-European roots.]
sextant