(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 9O¡, 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.