noun

• (geometry) An imaginary line around which an object spins (an axis of rotation) or is symmetrically arranged (an axis of symmetry).
• (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)
• (anatomy) The second cervical vertebra of the spine
• (anatomy) An imaginary, visualized plane separating two morphologically similar parts of an organism
• (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)
• (botany) The main stem or central part about which organs or plant parts such as branches are arranged
• (military) An alliance or coalition.
• (figurative) The centre of attention within a process (e.g. the axis of investigation)
• A deer native to Asia, of species Axis axis.
• The alliance (in effect before and during World War II) of Germany, Italy, Japan, and several minor allied countries, which opposed the Allies.