U

energy

noun, plural en·er·gies.

the capacity for vigorous activity; available power: I eat chocolate to get quick energy.
an adequate or abundant amount of such power: I seem to have no energy these days.
Often energies. a feeling of tension caused or seeming to be caused by an excess of such power: to work off one’s energies at tennis.
an exertion of such power: She plays tennis with great energy.
the habit of vigorous activity; vigor as a characteristic: Foreigners both admire and laugh at American energy.
the ability to act, lead others, effect, etc., forcefully.
forcefulness of expression: a writing style abounding with energy.
Physics. the capacity to do work; the property of a system that diminishes when the system does work on any other system, by an amount equal to the work so done; potential energy. Symbol: E
any source of usable power, as fossil fuel, electricity, or solar radiation.

noun plural -gies

intensity or vitality of action or expression; forcefulness
capacity or tendency for intense activity; vigour
vigorous or intense action; exertion
physics
1. the capacity of a body or system to do work
2. a measure of this capacity, expressed as the work that it does in changing to some specified reference state. It is measured in joules (SI units)Symbol: E
a source of powerSee also kinetic energy, potential energy

1590s, “force of expression,” from Middle French énergie (16c.), from Late Latin energia, from Greek energeia “activity, operation,” from energos “active, working,” from en “at” (see en- (2)) + ergon “work, that which is wrought; business; action” (see urge (v.)).

Used by Aristotle with a sense of “force of expression;” broader meaning of “power” is first recorded in English 1660s. Scientific use is from 1807. Energy crisis first attested 1970.

The capacity for work or vigorous activity; vigor; power.
The capacity of a physical system to do work.

The capacity or power to do work, such as the capacity to move an object (of a given mass) by the application of force. Energy can exist in a variety of forms, such as electrical, mechanical, chemical, thermal, or nuclear, and can be transformed from one form to another. It is measured by the amount of work done, usually in joules or watts. See also conservation of energy kinetic energy potential energy. Compare power work.

In physics, the ability to do work. Objects can have energy by virtue of their motion (kinetic energy), by virtue of their position (potential energy), or by virtue of their mass (see E = mc2).