The eighth part of a circle; an arc of 45 degrees.
- One eighth of a circle.
- A 45° arc.
- The area enclosed by two radii at a 45° angle and the intersected arc.
- An instrument based on the principle of the sextant but employing only a 45° angle, used as an aid in navigation.
- Astronomy The position of a celestial body when it is separated from another by a 45° angle.
- One of eight parts into which three-dimensional space is divided by three usually perpendicular coordinate planes.