QUAD'RANT, noun [Latin quadrans, a fourth.]

1. The fourth part; the quarter.

2. In geometry, the quarter of a circle; the arc of a circle containing ninety degrees; also, the space or area included between this arc and two radii drawn from the center to each extremity.

3. An instrument for taking the altitudes of the sun or stars, of great use in astronomy and navigation. Quadrants are variously made, but they all consist of the quarter of a circle whose limb is divided into ninety degrees; or, as in Hadley's reflecting quadrant an arc of forty five degrees is made to serve the same purpose as an arc of ninety degrees.

Quadrant of altitude, 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 is filled to the meridian and movable round to all points of the horizon. It serves as a scale in measuring altitudes, azimuths, etc.