Quadrant
(Quad"rant) n. [L. quadrans, -antis, a fourth part, a fourth of a whole, fr. quattuor four: cf. F.
quadrant, cadran. See Four, and cf. Cadrans.]
1. The fourth part; the quarter. [Obs.] Sir T. Browne.
2. (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.
3. (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.
4. 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.