Energy
Etymology
From Greek "energeia" — "en" (in) plus "ergon" (work) — coined by Aristotle for activity or being-at-work. It stayed a word for vigor until Thomas Young gave it its precise physical meaning in 1807, and the law that it is conserved was pieced together over the following decades.
noun · /EN-er-jee/
The capacity to do work or cause change, existing in forms — motion, heat, light, chemical bonds — that convert into one another but never vanish.
What it names
The single accounting unit behind everything that happens, letting you track a shared quantity as it changes costume from fuel to motion to heat.
Example
The chemical energy in the gasoline becomes the kinetic energy of the car and, through friction, ends up as waste heat.
Related idea
Energy is the capacity to do work; force is a push or pull. A force does no work — transfers no energy — unless it actually moves something.
noun · /EN-er-jee/
A person's liveliness or enthusiasm, or the emotional atmosphere they project — as in 'good energy' or 'she brings great energy.'
What it names
The felt vitality of a person or a room, a colloquial sense quite distinct from the physicist’s convertible capacity to do work.
Example
The new hire brought a burst of energy to the whole team.
Related idea
The felt vitality of a person or a room — 'good energy,' 'she brings great energy' — a colloquial cousin of charisma, quite apart from the physicist's convertible capacity to do work.