Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

sextant
     n 1: a unit of angular distance equal to 60 degrees
     2: a measuring instrument for measuring the angular distance
        between celestial objects; resembles an octant