Replenishment of drink briefly boosted long-term prisoner (5)
I believe the answer is:
lifer
'long-term prisoner' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lifer that I've seen before include "Person serving long sentence" , "One given lots of porridge" , "One behind bars for ever" , "Con" , "Prisoner serving the maximum term" .)