Energy

[en-er-jee] /ˈɛn ər dʒi/

noun, plural energies.
1.
the capacity for vigorous activity; available power:
I eat chocolate to get quick energy.
2.
an adequate or abundant amount of such power:
I seem to have no energy these days.
3.
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.
4.
an exertion of such power:
She plays tennis with great energy.
5.
the habit of vigorous activity; vigor as a characteristic:
Foreigners both admire and laugh at American energy.
6.
the ability to act, lead others, effect, etc., forcefully.
7.
forcefulness of expression:
a writing style abounding with energy.
8.
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; . Symbol: E.
9.
any source of usable power, as fossil fuel, electricity, or solar radiation.
/ˈɛnədʒɪ/
noun (pl) -gies
1.
intensity or vitality of action or expression; forcefulness
2.
capacity or tendency for intense activity; vigour
3.
vigorous or intense action; exertion
4.
(physics)

5.
a source of power See also kinetic energy, potential energy
n.

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.

energy en·er·gy (ěn’ər-jē)
n.

energy
(ěn’ər-jē)
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).

Note: The most important property of energy is that it is conserved — that is, the total energy of an isolated system does not change with time. This is known as the law of conservation of energy. Energy can, however, change form; for example, it can be turned into mass and back again into energy.