Free show on Five (9)
I believe the answer is:
vindicate
'free' is the definition.
(thesaurus)
'show on five' is the wordplay.
'show' becomes 'indicate' (synonyms).
'on' is a charade indicator (letters next to each other).
'five' becomes 'v' (roman numeral).
'indicate' after 'v' is 'VINDICATE'.
(Other definitions for vindicate that I've seen before include "Show to be right or justified" , "Successfully defend" , "Deflect criticism" , "Justify by evidence or results" , "Clear of blame" .)