octant

noun

1. the eighth part of a circle.
2. Mathematics. any of the eight parts into which three mutually perpendicular planes divide space.
3. an instrument having an arc of 24°, used by navigators for measuring angles up to 90°.
4. the position of one heavenly body when 45° distant from another.
5. (initial capital letter) Astronomy. the constellation Octans.

noun

1. maths
   1. any of the eight parts into which the three planes containing the Cartesian coordinate axes divide space
   2. an eighth part of a circle
2. astronomy the position of a celestial body when it is at an angular distance of 45° from another body
3. an instrument used for measuring angles, similar to a sextant but having a graduated arc of 45°

n.instrument for making angular measurements in navigation or astronomy, 1731, from Late Latin octans “the eighth part,” from octo “eight” (see octa-) on analogy of quadrant. In geometry, octant meant “the eighth part of a circle.”