Definition of: octant

(ok′tənt) noun
1. An eighth part of a circle; an arc subtending an angle of 45 degrees.
2. Astron. The position in the heavens that is one eighth of a circle distant from conjunction or quadrature; one of the four positions of the moon midway between new or full moon and quarters.
3. An instrument resembling a sextant but having an arc of only 45 degrees: used for measuring the angular height of the sun, moon, and other celestial bodies as an aid in navigation.
4. Geom. One of the eight trihedral compartments of space formed by three planes with the three axes, x, y, and z, of a Cartesian coordinate system as edges. [<LL octans an eighth part <L octo eight]
—oc·tant′al (-tan′təl) adjective
CARTESIAN OCTANT
O. Origin. Coordinates of A: x = 4, = y = 7, z = 5; of B; x = 4, y = 7.