Definition of "octant" [oc•tant]

• One eighth of a circle. (noun)
• A 45° arc. (noun)
• The area enclosed by two radii at a 45° angle and the intersected arc. (noun)
• An instrument based on the principle of the sextant but employing only a 45° angle, used as an aid in navigation. (noun)
• Astronomy The position of a celestial body when it is separated from another by a 45° angle. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "John Paul’s deliverance from the hardship of the lower deck was a brass instrument called an octant."
• "Advances in the development of these instruments made such calculations easier and more precise, for example: the "course protractor", the "cuadrant", the "octant and the sextant", and the "longitude clock", which was a precision chronometer."
• "From a private collection, offerings include several important pairs of globes by Newton, a sextant by Ramsden, an octant by George Jones, equinoctial dials, astrolabes, chronometers, microscopes and nautical antiques."