Energy

en·er·gy /ˈenərjē/

noun

1.

the strength and vitality required for sustained physical or mental activity. "changes in the levels of vitamins can affect energy and well-being" (Similar: vitality, vigor, life, liveliness, animation, vivacity, spirit)

2.

power derived from the utilization of physical or chemical resources, especially to provide light and heat or to work machines.

"nuclear energy"