1. (n.) The fourth part; the quarter.

2. (n.) 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. (n.) One of the four parts into which a plane is divided by the coordinate 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. (n.) 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.

adjunct astrolabe azimuth circle azimuth compass bevel bevel protractor bevel square clinometer component contingent crescent cross section detachment detail division dole fraction goniometer graphometer half circle hemicycle installment item pantometer parcel part particular percentage portion protractor quarter quota radiogoniometer random sample remainder sample sampling section sector segment semicircle sextant share subdivision subgroup subspecies theodolite transit transit circle transit instrument transit theodolite