The axis about which any body rotates. / The line joining the North Pole and South Pole about which the Earth rotates daily.

(mathematics) The line containing the locus of points from which the segments respectively tangent to two given circles have equal length.

(mathematics) The vertical line in the complex plane, every point on which corresponds to a complex number having zero real component

(mathematics) The horizontal line in the complex plane, every point on which corresponds to a real number

(mathematics, geometry) One of the lines in the coordinate system that represents one of the dimensions.

plural of axis cylinder

(biology, dated) An axon.

(chiefly in the plural) A country in the alliance (in effect before and during World War II) of Nazi Germany, fascist Italy, imperial Japan, and a few other countries, which opposed the Allies.

The optical axis of an eye (extending from the viewed object through the centre of the pupil to the yellow spot of the retina)

(geometry) Half of the major axis of a circle or ellipse. / (geometry) Half of the distances between the two branches of a hyperbola.