means A change from one state, position, or arrangement to another — or a defined block of working time during which one set of workers replaces another.

from From Old English 'sciftan,' to arrange, divide, or apportion, with cousins in Old Norse 'skipta' (to divide) and related Germanic words. The earliest sense was about ordering and separating things; from there it drifted toward 'changing or moving,' since to rearrange is to make things move. The 'work shift' sense grew from the idea of one group relieving or replacing another, and the loose undergarment called a 'shift' got its name because you changed it — you shifted into a fresh one.