en•er•gy (ěn'ər-jē)
-noun, plural -gies.

1. The capacity for vigorous activity; available power. 
   
   
   
2. An adequate or abundant amount of such power. 
   
   
   
3. An exertion of such power.
   
   
   
4. The ability to act, lead others, effect, etc., forcefully.
   
   
   
5. Any source of usable power.