axis

Etymology 1

Borrowed from Latin axis (“axle, axis”) in the 16th century. Doublet of axle.

noun

1. (geometry) An imaginary line around which an object spins (an axis of rotation) or is symmetrically arranged (an axis of symmetry).
   A doorknob of whatever roundish shape is effectively a continuum of levers, with the axis of the latching mechanism—known as the spindle—being the fulcrum about which the turning takes place. 2012-03, Henry Petroski, “Opening Doors”, in American Scientist, volume 100, number 2, pages 112–3
   The Earth rotates once a day on its axis
2. (mathematics) A fixed one-dimensional figure, such as a line or arc, with an origin and orientation and such that its points are in one-to-one correspondence with a set of numbers; an axis forms part of the basis of a space or is used to position and locate data in a graph (a coordinate axis)
3. (anatomy) The second cervical vertebra of the spine
4. (anatomy) An imaginary, visualized plane separating two morphologically similar parts of an organism
5. (psychiatry) A form of classification and descriptions of mental disorders or disabilities used in manuals such as the DSM (Diagnostic and Statistical Manual of Mental Disorders)
6. (botany) The main stem or central part about which organs or plant parts such as branches are arranged
7. (military) An alliance or coalition.
   This Berlin-Rome vertical line is not an obstacle but rather an axis around which can revolve all those European states with a will to collaboration and peace. 1936, November 1st, Benito Mussolini, Milan Speech

Etymology 2

From Latin, name of an Indian animal mentioned by the Roman senator Pliny.

noun

1. A deer native to Asia, of species Axis axis.