/ ˈenədʒi; NAmE -ərdʒi/ noun
1.
[ U ] the ability to put effort and enthusiasm into an activity, work, etc. :
It's a waste of time and energy.
She's always full of energy .
nervous energy (= energy produced by feeling nervous)
2.
energies [ pl. ] the physical and mental effort that you use to do sth :
She put all her energies into her work.
creative / destructive energies
3.
[ U ] a source of power, such as fuel, used for driving machines, providing heat, etc. :
solar / nuclear energy
It is important to conserve energy.
an energy crisis (= for example when fuel is not freely available)
4.
[ U ] ( physics ) the ability of matter or radiation to work because of its mass, movement, electric charge, etc. :
kinetic / potential, etc. energy
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WORD ORIGIN
mid 16th cent. (denoting force or vigour of expression): from French énergie , or via late Latin from Greek energeia , from en- in, within + ergon work.