Wordnet 3.0
NOUN (1)
1. 
 a definite stable energy that a physical system can have; 
 used especially of the state of electrons in atoms or molecules; 
- Example: "according to quantum theory only certain energy levels are possible"[syn: energy level, energy state]
WordNet (r) 3.0 (2006):
energy level
    n 1: a definite stable energy that a physical system can have;
         used especially of the state of electrons in atoms or
         molecules; "according to quantum theory only certain energy
         levels are possible" [syn: energy level, energy state]