δύναμις

Dýnamis in Greek means power, force, or ability. Aristotle used it as a philosophical term for potentiality — the capacity to become or to act, as opposed to energeia (actuality). The word was abstract for two thousand years. It named a concept, not a machine. The jump from philosophy to engineering happened in the nineteenth century.

Michael Faraday discovered electromagnetic induction in 1831: moving a magnet through a coil of wire generates electric current. The machine that does this — a rotating coil in a magnetic field — was called a dynamo. The word was first used in this sense by the German manufacturer Siemens in the 1860s, from the Greek dynamis (power). A dynamo converts mechanical motion into electrical power. The abstract Greek word became a concrete English machine.

The dynamo transformed civilization. Edison's Pearl Street Station in New York (1882) used dynamos to generate electricity for the first commercial power grid. Within a generation, dynamos powered streetcars, factories, and homes. The word was synonymous with electrical generation until the mid-twentieth century, when 'generator' replaced it in technical usage.

The figurative meaning arrived quickly. A dynamo is any person or thing that generates energy, ideas, or activity. 'She's a dynamo.' 'A dynamo of creativity.' The word carries the image of ceaseless rotation producing ceaseless output. Alfred Nobel named his explosive 'dynamite' in 1867 from the same Greek root — a different kind of power, equally world-changing.