quadrant

noun

1. region of the plane defined by the axes of a two-dimensional Cartesian system
2. an instrument for measuring altitudes consisting commonly of a graduated arc of 90 degrees with an index or vernier and usually having a plumb line or spirit level for fixing the vertical or horizontal direction
3. a device or mechanical part shaped like or suggestive of the quadrant of a circle
4. Circular sector with central angle 90°; one fourth of a full circle