axis

ax·is / ˈaksis/ • n. (pl. ax·es / ˈaksēz/ ) 1. an imaginary line about which a body rotates: the earth revolves on its axis once every 24 hours. ∎ Geom. an imaginary straight line passing through the center of a symmetrical solid, and about which a plane figure can be conceived as rotating to generate the solid. ∎  an imaginary line that divides something into equal or roughly equal halves, esp. in the direction of its greatest length. 2. Math. a fixed reference line for the measurement of coordinates: the horizontal axis. 3. a straight central part in a structure to which other parts are connected. ∎  Bot. the central column of an inflorescence or other growth. ∎  Zool. the skull and backbone of a vertebrate animal. 4. Anat. the second cervical vertebra, below the atlas at the top of the backbone. 5. an agreement or alliance between two or more countries that forms a center for an eventual larger grouping of nations: the Anglo-American axis. ∎  (the Axis) the alliance of Germany and Italy formed before and during World War II, later extended to include Japan and other countries: [as adj.] the Axis Powers.