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

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

The brain and the spinal cord

(anatomy) Synonym of cerebrospinal axis

The spin axis of a freely rotating body. In the case of the Earth, it differs from the figure axis by a few meters. This difference being a partial cause of the Earth's wobble.

The symmetrical axis of a body. In the case of the Earth, it differs from the rotational axis by a few meters, and so is a partial cause of the Earth's wobble.

(optics) An imaginary line within an optical system around which there is rotational symmetry.

The shortest diameter of an ellipse, which bisects the major axis at a right angle.

A chord progression, I–V–vi–IV, used in Western popular music, common since the 1970s.

Alternative form of axisymmetric