en·er·gy 
(ĕnər-jē)
(ĕnər-jē)n. pl. en·er·gies
1. The capacity for work or vigorous activity: Who has the energy to climb that trail? See Synonyms at strength.
2.
a. also energies Exertion of vigor or power: a project requiring a great deal of time and energy; devoted her energies to writing songs.
b. Vitality and intensity of expression: a speech delivered with energy and emotion.
c. Informal A nonphysical force or quality perceived as inhering in a particular place, person, or situation: was turned off by the group's negative energy.
3.
a. Usable heat or power: Each year Americans consume a high percentage of the world's energy.
b. A source of usable power, such as petroleum or coal.
4. Physics
a. The capacity of a physical system to do work.
b. A form, amount, or level of this capacity: "a searing beam of 30 trillion protons, with energies up to 50 million electronvolts" (Science News).
[French énergie, from Late Latin energīa, from Greek energeia, from energos, active : en-, in, at; see EN-2 + ergon, work; see werg- in the Appendix of Indo-European roots.]