Fallen angel (5)
I believe the answer is:
satan
'fallen angel' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for satan that I've seen before include "arch-fiend" , "Fallen archangel" , "Old Nick, Lucifer or Beelzebub" , "The devil, Beelzebub" , "Diabolical figure" .)