Octant

1. (n.) The eighth part of a circle; an arc of 45 degrees.
2. (n.) The position or aspect of a heavenly body, as the moon or a planet, when half way between conjunction, or opposition, and quadrature, or distant from another body 45 degrees.
3. (n.) An instrument for measuring angles (generally called a quadrant), having an arc which measures up to 9Oˇ, but being itself the eighth part of a circle. Cf. Sextant.
4. (n.) One of the eight parts into which a space is divided by three coordinate planes.