1. One eighth of a circle.
a. A 45° arc.
b. The area enclosed by two radii at a 45° angle and the intersected arc.
3. An instrument based on the principle of the sextant but employing only a 45° angle, used as an aid in navigation.
4. Astronomy The position of a celestial body when it is separated from another by a 45° angle.
5. One of eight parts into which three-dimensional space is divided by three usually perpendicular coordinate planes.
[Latin octāns, octant-, from octō, eight; see oktō(u) in the Appendix of Indo-European roots.]
oc·tantal (ŏk-tăntəl) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.