Excellent form of punishment (4)
I believe the answer is:
fine
I believe this clue is a double definition.
'excellent' is the first definition.
(synonyms)
'form of punishment' is the second definition.
(someone may be fined as a punishment)
(Other definitions for fine that I've seen before include "nice > brandy" , "Very thin - excellent?" , "Sheer or very good" , "Super" , "A monetary penalty - sounds great" .)