\Oc"tant\, n. [L. octans, -antis. fr. octo eight. See
{Octave}.]
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
   quadrant), having an arc which measures up to 9O[deg], but
   being itself the eighth part of a circle. Cf. {Sextant}.
4. (Math. & Crystallog.) One of the eight parts into which a
   space is divided by three co["o]rdinate planes.