Better than prison? Jolly good! (4)
I believe the answer is:
fine
'good' is the definition.
(both can mean satisfactory)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for fine that I've seen before include "Sheer or very good" , "Excellent kind of monetary penalty" , "Acceptable - punishment" , "Money penalty is clear and dry" , "Dry and sunny" .)