- 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.
- 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.
- one of the four quarters of the horoscope: determined by the ascendant, nadir, descendant, and midheaven and numbered counterclockwise from the ascendant.
- one of two metal sliding pieces, of quadrant form, used to support the fall front of a desk from above.
- geometry
- a quarter of the circumference of a circle
- the area enclosed by two perpendicular radii of a circle and its circumference
- any of the four sections into which a plane is divided by two coordinate axes
- a piece of a mechanism in the form of a quarter circle, esp one used as a cam or a gear sector
- 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
