eax

Eax in Old English meant an axle — the shaft on which a wheel rotates. The word descends from Proto-Germanic *ahsō, from Proto-Indo-European *h₂eḱs- (axle, axis). Latin axis and Sanskrit ákṣa come from the same root. The word for the shaft that holds a wheel is shared across a language family that stretches from India to Iceland, suggesting that the technology and the word traveled together.

The earliest known wheeled vehicles date to around 3500 BCE in the Pontic-Caspian steppe. The axle was the invention that made the wheel useful — a wheel without an axle is a millstone, not transportation. The fixed axle (wheel rotates on the axle) and the rotating axle (axle turns with the wheel) are the two basic designs, and both appeared early. The choice between them shaped four thousand years of vehicle engineering.

Medieval wagons and carriages used wooden axles greased with animal fat. Iron axles appeared in the eighteenth century. Steel axles in the nineteenth. The front axle of an automobile must allow the wheels to turn at different speeds around corners — the differential, invented by various engineers in the nineteenth century, solved this problem. The axle is the component that connects power to ground.

The word 'axle' is now mostly technical. It appears in automotive engineering, railway engineering, and heavy machinery. The figurative use of 'axis' (from the same root) is more common — the axis of a graph, the axis of a debate, the axis of the Earth. Both words describe the central line around which everything else organizes.