1an imaginary line about which a body rotates:the Earth revolves on its axis once every 24 hours
Geometry an imaginary straight line passing through the centre of a symmetrical solid, about which a plane figure can be conceived as rotating to generate the solid.
an imaginary line which divides something into equal or roughly equal halves, especially in the direction of its greatest length.
2 Mathematics a fixed reference line for the measurement of coordinates:the variable that is thought of as a cause is placed on the horizontal axis, and the variable that is thought of as an effect on the vertical axis
3a straight central part in a structure to which other parts are connected.
Botany the central column of an inflorescence or other growth:the leaflets are arranged in rows on a slender axis
Zoology the skull and backbone of a vertebrate animal.
4 Anatomy the second cervical vertebra, below the atlas at the top of the backbone.
5an agreement or alliance between two or more countries that forms a centre for an eventual larger grouping of nations:the Anglo-American axis
(the Axis) the alliance of Germany and Italy formed before and during the Second World War, later extended to include Japan and other countries: [as modifier]:the Axis Powers