| n. | 1. | (Geom.) The eighth part of a circle; an arc of 45 degrees. |
| 2. | (Astron. & Astrol.) 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. | An instrument for measuring angles (generally called a | |
| 4. | (Math. & Crystallog.) One of the eight parts into which a space is divided by three coördinate planes. |
| Noun | 1. | octant - a measuring instrument for measuring angles to a celestial body; similar to a sextant but with 45 degree calibration |