octantal

octant

[ok-tuhnt]
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.

Origin:
1680–90; < Latin octant- (stem of octāns); see Octans

octantal [ok-tan-tl] , adjective
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World English Dictionary
octant (ˈɒktənt)
 
n
1.  maths
 a.  any of the eight parts into which the three planes containing the Cartesian coordinate axes divide space
 b.  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°
 
[C17: from Latin octans half quadrant, from octo eight]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

octant
"instrument for making angular measurements in navigation or astronomy," 1731, from L.L. octans, from octo "eight" (see octa-).
Online Etymology Dictionary, © 2010 Douglas Harper
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