relating to or around a real or imaginary straight line going through the centre of an object that is spinning, or a line that divides a symmetrical shape into two equal halves
(IN THE BODY)
anatomy（身体）中心线的
relating to an imaginary line through the centre of the body
anatomy枢椎的，第二颈椎的
relating to the axis(= the second of the small bones in the neck that form the spine and support the skull)