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The Collaborative International Dictionary

Octant \Oc"tant\, n. [L. octans, -antis. fr. octo eight. See Octave.]

  1. (Geom.) The eighth part of a circle; an arc of 45 degrees.

  2. (Astron. & Astrol.) 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.

  3. An instrument for measuring angles (generally called a quadrant), having an arc which measures up to 9O[deg], but being itself the eighth part of a circle. Cf. Sextant.

  4. (Math. & Crystallog.) One of the eight parts into which a space is divided by three co["o]rdinate planes.

Douglas Harper's Etymology Dictionary

instrument for making angular measurements in navigation or astronomy, 1731, from Late Latin octans "the eighth part," from octo "eight" (see octa-) on analogy of quadrant. In geometry, octant meant "the eighth part of a circle."


n. 1 The eighth part of a circle; an arc of 45 degrees. 2 (context geometry English): The eighth part of a disc; a sector of 45 degrees; half a quadrant. 3 (context nautical English): An instrument for measuring angles, particularly of elevation.


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

Octant (plane geometry)

In plane geometry, octant is a circular sector obtained by division of the full circle into 8 equal parts, hence the name. It is a sector with the central angle of 45°.


Octant may refer to:

  • Octant (plane geometry), 1/8th of the full circle
  • Octant (solid geometry), one of the 8 divisions of the 3-D space by coordinate planes
  • Octant (circle), a circular segment
  • Octant (instrument) for celestial navigation
  • The Octant, constellation Octans
  • Octant (band), from Seattle, Washington
Octant (instrument)

The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.

Octant (band)

Octant is an experimental noise rock band formed in 1999 in Washington State. They created two full-length albums which were released on Up Records. The band was a duo led by multi-instrumentalist and instrument-designer Matt Steinke. Tassany Zimmerman primarily played electric synthesizer. Octant's live show included an electro-mechanical automated drum machine. This machine was designed and built by Matt Steinke.

In 2010, Matt Steinke announced a Kickstarter for a new Octant record. Zimmerman was not involved. The self-titled album was released on January 15, 2011.

Octant (solid geometry)

An octant in solid geometry is one of the eight divisions of a Euclidean three-dimensional coordinate system defined by the signs of the coordinates. It is similar to the two-dimensional quadrant and the one-dimensional ray.

The generalization of an octant is called orthant.

Usage examples of "octant".

Torve the Trog was eating from a heaping plate of kumquats, Morovian sugar-grass, and ruvelo, a red root-paste common in this octant as a staple starch.

Sailors could tell their latitude by the angle of the sun off the horizon, had been doing it for a thousand years with cross-staffs, astrolabes, octants and sextants.

There were no instruments in the taxi, no built-in octants, no patent logs, no computers.