Lucifer's former prison (3,4)
I believe the answer is:
old nick
'lucifer's' is the definition.
(synonyms)
'former prison' is the wordplay.
'former' becomes 'old' (both can mean previous).
'prison' becomes 'nick' (slang term for prison).
'old'+'nick'='OLD NICK'
(Other definitions for old nick that I've seen before include "The Dickens" , "Mephisto" , "'The prince of darkness (3,4)'" , "Familiar name for the devil, ancient chap" , "cut from long ago?" .)