Definition of octant in US English:



  • 1An arc of a circle equal to one eighth of its circumference, or the area enclosed by such an arc with two radii of the circle.

    • ‘Included in those downloads are the last two octants needed to complete the color, 360-degree ‘mission success' panorama.’
    • ‘The arc was extended from an octant to a sextant and a stout handle was added at the back of the instrument.’
    1. 1.1 Each of eight parts into which a space or solid body is divided by three planes which intersect (especially at right angles) at a single point.
      • ‘At the octant (eight-cell) stage the embryo proper and suspensor are clearly distinct.’
      • ‘The model put forward for the action of BDL suggests that auxin is involved in determining hypophyseal cell fate at the octant stage.’
    2. 1.2 An obsolete instrument in the form of a graduated eighth of a circle, used in astronomy and navigation.
      • ‘Clark used celestial observation to determine latitude, triangulating position with an octant.’
      • ‘Instead of compasses, octants, and two-pole chains, modern digital GPS units determine position and direction.’


Late 17th century: from Latin octans, octant- ‘half-quadrant’, from octo ‘eight’.