(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.