I believe the answer is:
'lucifer' is the definition.
(I know that lucifer can be written as Satan)
This is the entire clue.
(Other definitions for satan that I've seen before include "The devil, Beelzebub" , "Fallen archangel" , "Diabolical figure" , "Fiend" , "Old Nick, Lucifer or Beelzebub" .)