Satan's scar? (3,4)
I believe the answer is:
old nick
This might be a double definition.
'satan's' is the first definition.
(synonyms)
'scar?' is the second definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
Can you help me to learn more?
(Other definitions for old nick that I've seen before include "Newgate's" , "Newgate or Marshalsea?" , "The Evil One" , "spirit of evil" , "Mephisto" .)