1. astronomy eighth of astronomical circle: the position of one body in the sky one-eighth of a circle (45°) from another
2. mathematics eighth of circle: one-eighth of a circle, with or without the enclosed area
3. mathematics region of space in Cartesian system: any one of the eight regions into which space is divided by the three planes of the Cartesian coordinate system
[Late 17th century. < Latin octant- "half-quadrant" < octo (see octo-)]
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