a quarter of a circle; an arc of 90°.
the area included between such an arc and two radii drawn one to each extremity.
something shaped like a quarter of a circle, as a part of a machine.
Geometry, Astronomy. one of the four parts into which a plane, as the face of a heavenly body, is divided by two perpendicular lines, numbered counterclockwise from upper right: the first quadrant of the moon.
an instrument, usually containing a graduated arc of 90°, used in astronomy, navigation, etc., for measuring altitudes.
Astrology. one of the four quarters of the horoscope: determined by the ascendant, nadir, descendant, and midheaven and numbered counterclockwise from the ascendant.
Furniture. one of two metal sliding pieces, of quadrant form, used to support the fall front of a desk from above.

1350–1400; Middle English < Latin quadrant- (stem of quadrāns) fourth part

quadrantal [kwo-dran-tl] , adjective
quadrantlike, adjective
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World English Dictionary
quadrant (ˈkwɒdrənt)
1.  geometry
 a.  a quarter of the circumference of a circle
 b.  the area enclosed by two perpendicular radii of a circle and its circumference
 c.  any of the four sections into which a plane is divided by two coordinate axes
2.  a piece of a mechanism in the form of a quarter circle, esp one used as a cam or a gear sector
3.  an instrument formerly used in astronomy and navigation for measuring the altitudes of stars, consisting of a graduated arc of 90° and a sighting mechanism attached to a movable arm
[C14: from Latin quadrāns a quarter]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

late 14c., "a quarter of a day, six hours," from L. quadrantem (nom. quadrans) "fourth part," prop. prp. of quadrare "to make square," from quadrus "a square," from quattuor "four" (see four). Sense of "measuring instrument" is first recorded c.1400, so called because it forms a quarter circle.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

quadrant quad·rant (kwŏd'rənt)

  1. A circular arc of 90 degrees; one fourth of the circumference of a circle.

  2. A quarter portion of any roughly circular anatomical area such as the abdomen, measuring along imaginary axes at right angles to each other.

quad·ran'tic (kwŏ-drān'tĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
quadrant   (kwŏd'rənt)  Pronunciation Key 
  1. An arc equal to one quarter of the circumference of a circle; an arc of 90°.

  2. Any of the four regions into which a plane is divided by the axes of a Cartesian coordinate system. The quadrants are numbered counterclockwise one through four, beginning with the quadrant in which both the x- and y-coordinates are positive (usually the upper right quadrant).

  3. A navigational instrument similar to a sextant but with an arc of 90° rather than 60°. See more at sextant.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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