n.
 (pl. energies)
   - the strength and vitality required for sustained activity. 
▸
(energies)
 a person's physical and mental powers as applied to a particular activity.
 - power derived from physical or chemical resources to provide light and heat or to work machines.
 - Physics  the property of matter and radiation which is manifest as a capacity to perform work.
 
 
  Etymology
  C16: from Fr. énergie, or via late L. from Gk energeia, from en- ‘in, within’ + ergon ‘work’.