Underhand, dodgy character promoting energy (5)
I believe the answer is:
sneak
'underhand' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for sneak that I've seen before include "Telltale; furtive person" , "Snitcher" , "To go stealthily" , "Go furtively - inform on another child" , "Move furtively - tell tales" .)