[ok-tuh nt]


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

Nearby words

  1. octanedioic acid,
  2. octangle,
  3. octangular,
  4. octanoic acid,
  5. octans,
  6. octantal,
  7. octantis,
  8. octarchy,
  9. octaroon,
  10. octastyle

Origin of octant

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

Related formsoc·tan·tal [ok-tan-tl] /ɒkˈtæn tl/, adjective

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for octant

British Dictionary definitions for octant



  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
astronomy the position of a celestial body when it is at an angular distance of 45° from another body
an instrument used for measuring angles, similar to a sextant but having a graduated arc of 45°

Word Origin for octant

C17: from Latin octans half quadrant, from octo eight

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for octant



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."

Online Etymology Dictionary, © 2010 Douglas Harper