quadrant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A circular arc of 90°; one fourth of the circumference of a circle.
• noun The plane area bounded by such an arc and two perpendicular radii.
• noun Any of the four areas into which a plane is divided by the reference axes in a Cartesian coordinate system, designated first, second, third, and fourth, counting counterclockwise from the area in which both coordinates are positive.
• noun A machine part or other mechanical device that is shaped like a quarter circle.
• noun An early instrument for measuring altitude of celestial bodies, consisting of a 90° graduated arc with a movable radius for measuring angles.

from The Century Dictionary.

• Square.
• noun In embryology, one of the four blastomeres or cleavage-cells in the four-cell stage of the ovum.
• noun A square or one of its sides.
• noun An oscillating arm attached to a spinning-mule to give a proper rotation to the spindles during the winding of the yarn on the cop.
• noun The fourth part; the quarter.
• noun The quarter of a circle; the arc of a circle containing 90°; also, the figure included between this arc and two radii drawn from the center to each extremity; the division of angular magnitude from zero to a right angle, or 90°.
• noun An astronomical instrument for measuring altitudes, of ancient origin, and consisting of a graduated arc of 90°, with a movable radius carrying sights, or the quadrant, carrying sights, might turn about a fixed radius.
• noun An instrument of navigation, for measuring the altitude of the sun, distinctively called the reflecting quadrant.
• noun An instrument used in giving a cannon or mortar the angle of elevation necessary to the desired range.
• noun In electricity, a name suggested for the practical unit of self-induction. Its value is 10 centimeters.
• Four-sided; square.

from the GNU version of the Collaborative International Dictionary of English.

• noun obsolete The fourth part; the quarter.
• noun (Geom.) The quarter of a circle, or of the circumference of a circle, an arc of 90°, or one subtending a right angle at the center.
• noun (Anal. (Geom.) One of the four parts into which a plane is divided by the coördinate axes. The upper right-hand part is the first quadrant; the upper left-hand part the second; the lower left-hand part the third; and the lower right-hand part the fourth quadrant.
• noun An instrument for measuring altitudes, variously constructed and mounted for different specific uses in astronomy, surveying, gunnery, etc., consisting commonly of a graduated arc of 90°, with an index or vernier, and either plain or telescopic sights, and usually having a plumb line or spirit level for fixing the vertical or horizontal direction.
• noun an instrument consisting of a graduated limb, with a plumb line or spirit level, and an arm by which it is applied to a cannon or mortar in adjusting it to the elevation required for attaining the desired range.
• noun See Gunter's quadrant, in the Vocabulary.
• noun a hand instrument used chiefly at sea to measure the altitude of the sun or other celestial body in ascertaining the vessel's position. It consists of a frame in the form of an octant having a graduated scale upon its arc, and an index arm, or alidade pivoted at its apex. Mirrors, called the index glass and the horizon glass, are fixed one upon the index arm and the other upon one side of the frame, respectively. When the instrument is held upright, the index arm may be swung so that the index glass will reflect an image of the sun upon the horizon glass, and when the reflected image of the sun coincides, to the observer's eye, with the horizon as seen directly through an opening at the side of the horizon glass, the index shows the sun's altitude upon the scale; -- more properly, but less commonly, called an octant.
• noun an appendage of the artificial globe, consisting of a slip of brass of the length of a quadrant of one of the great circles of the globe, and graduated. It may be fitted to the meridian, and being movable round to all points of the horizon, serves as a scale in measuring altitudes, azimuths, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One of the four sections made by dividing an area with two perpendicular lines.
• noun mathematics The four regions of the Cartesian plane bounded by the x-axis and y-axis.
• noun geometry One fourth of a circle or disc; a sector with an angle of 90°.
• noun nautical A measuring device with a graduated arc of 90° used in locating an altitude.

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

• noun a measuring instrument for measuring altitude of heavenly bodies
• noun a quarter of the circumference of a circle
• noun the area enclosed by two perpendicular radii of a circle
• noun any of the four areas into which a plane is divided by two orthogonal coordinate axes