Prisoner left fire spreading (5)
I believe the answer is:
lifer
'prisoner' is the definition.
(prisoner serving a life sentence)
'left fire spreading' is the wordplay.
'left' becomes 'l' (common abbreviation).
'spreading' indicates an anagram.
'fire' anagrammed gives 'ifer'.
'l'+'ifer'='LIFER'
(Other definitions for lifer that I've seen before include "Prisoner serving the maximum term" , "One behind bars for ever" , "person given sizeable bird" , "One with maximum sentence" , "Convicted murderer, say" .)