Old Nick had life back (5)
I believe the answer is:
devil
'old nick' is the definition.
(synonyms)
'had life back' is the wordplay.
'had life' becomes 'lived' ('live' can be a synonym of 'have life').
'back' says the letters should be written backwards.
'lived' in reverse letter order is 'DEVIL'.
(Other definitions for devil that I've seen before include "Archfiend" , "Wicked spirit" , "Lived with Satan" , "Evil supernatural being" , "Fiend" .)