axis1

noun (plural axes /-siːz/)

• 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