Ax'is, the straight line, real or imaginary, passing through a body or magnitude, on which it revolves, or may be supposed to revolve; for instance, the axis of the earth, the imaginary line drawn through its two poles. In botany the word is also used, the stem being termed the ascending axis, the root the descending axis. In anatomy the name is given to the second vertebra from the head, that on which the atlas moves. In mathematics an axis is the straight line about which the parts of a figure or body are symmetrically arranged.