from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. One eighth of a circle.
  • n. A 45° arc.
  • n. The area enclosed by two radii at a 45° angle and the intersected arc.
  • n. An instrument based on the principle of the sextant but employing only a 45° angle, used as an aid in navigation.
  • n. Astronomy The position of a celestial body when it is separated from another by a 45° angle.
  • n. One of eight parts into which three-dimensional space is divided by three usually perpendicular coordinate planes.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The eighth part of a circle; an arc of 45 degrees.
  • n. : The eighth part of a disc; a sector of 45 degrees; half a quadrant.
  • n. : An instrument for measuring angles, particularly of elevation.

from the GNU version of the Collaborative International Dictionary of English

  • n. The eighth part of a circle; an arc of 45 degrees.
  • n. The position or aspect of a heavenly body, as the moon or a planet, when half way between conjunction, or opposition, and quadrature, or distant from another body 45 degrees.
  • n. An instrument for measuring angles (generally called a quadrant), having an arc which measures up to 9O°, but being itself the eighth part of a circle. Cf. Sextant.
  • n. One of the eight parts into which a space is divided by three coördinate planes.

from The Century Dictionary and Cyclopedia

  • n. The eighth part of a circle.
  • n. In astronomy, that position or aspect of two heavenly bodies, especially a planet and the sun, when half-way between conjunction or opposition and quadrature, or distant from one another by the eighth part of a circle, or 45°.
  • n. An instrument used by seamen for measuring angles, resembling a sextant or quadrant in principle, but having an arc the eighth part of a circle, or 45°. By double reflection it can measure an arc of 90°. See sextant. Hadley's quadrant is really an octant.
  • n. Each of the eight regions into which space is divided by three copunctal non-costraight planes.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a measuring instrument for measuring angles to a celestial body; similar to a sextant but with 45 degree calibration


Latin octāns, octant-, from octō, eight; see oktō(u) in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin octans (Wiktionary)


  • John Paul’s deliverance from the hardship of the lower deck was a brass instrument called an octant.

    John Paul Jones

  • 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.

    Sailing on and on

  • 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.

    Useful and Beautiful Devices | clusterflock

  • It was in its octant, and showed a crescent finely traced on the dark background of the sky.

    Round the Moon

  • Curved an eighth of circle, hence “octant”, fixed with small mirrors and etched by degrees, an octant can tell a mariner the angle of the sun to the horizon at high noon.

    John Paul Jones

  • Wesley found a packet of small iron tools, an octant and a massive spiked club.


  • Charred remains of the boat, a burned octant, and a few unexploded cartridges were all that remained of the meager outfit upon which they depended to take them to the mouth of the river, a distance of over 250 miles.

    Scientific American Supplement No. 822, October 3, 1891

  • Used the octant on some sunshots; used the drift meter on the whitecaps; picked up wind changes; made heading corrections; came in "on target" with less than ½ hour fuel remaining.

    Diary of Lt. David Purner

  • It is the sextant or some member of the sextant family -- such as the quadrant, octant, etc.

    Lectures in Navigation

  • Ismailoff gave Cook letters for the Governor of Kamtschatka and the Commandant of Petropaulowsk; and Cook, finding “he was tolerably well versed in astronomy,” gave him a Hadley's octant, and though it was the first one he had seen, he soon made himself acquainted with its uses.

    The Life of Captain James Cook

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  • "Octant or octile, in astronomy, the aspect of two planets, wherein they are distant an eight part of a circle, or 45 degrees from each other."
    Falconer's New Universal Dictionary of the Marine (1816), 326

    October 14, 2008