Possibly large fine! (5)
I believe the answer is:
regal
'fine' is the definition.
(thesaurus)
'possibly large' is the wordplay.
'possibly' is an anagram indicator.
'large' is an anagram of 'REGAL'.
(Other definitions for regal that I've seen before include "Fit for a king" , "Showing great dignity" , "King-like" , "Royal - 5 down (anag)" , "Portable organ" .)