Punishment for being thin? (4)
I believe the answer is:
fine
This clue is a double definition.
'punishment' is the first definition.
(fine is a kind of punishment)
'being thin?' is the second definition.
('fine' can be similar in meaning to 'thin')
'for' acts as a link.
(Other definitions for fine that I've seen before include "Penalty; exalted; brandy" , "Splendid - financial penalty" , "nearly in line with wicket" , "Sunny -- penalty" , "Very thin - excellent?" .)