[ ok-tuh nt ]
/ ˈɒk tənt /


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.

Origin of octant

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

Related forms

oc·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


/ (ˈɒktənt) /


  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