The most common and most likely answer to this crossword clue is the 5 letter word LIFER
L
I
F
E
R
More clues leading to the result LIFER
- I’m unlikely to get out rifle which has been discharged
- Prisoner is old thief — time to be released
- Curtailment of second drink upset prisoner
- Second drink shortly brought up for prisoner
- Prisoner’s fresh charge briefly withdrawn
- Judge — extremely illiberal — hauled up prisoner
- Prisoner, one fellow held by the French King
- Stiff punishment to top up endlessly, being sent back
- . Current judge retires after initially libelling prisoner
- Most essential part of ruling judge overturned, as convict given longest sentence
Buddy explains!

The straight part
We know that "Stiff punishment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stiff punishment = lifer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LIFER mean?
LIFER noun- A prisoner sentenced to life in prison.
- A prisoner sentenced to transportation for life.
- A person with a singular career path, especially in the military.
- A bird species seen for the first time by a birder who is keeping a list of all the species he or she has ever seen.