Detective with charge that's appropriate (6)
I believe the answer is:
pirate
'appropriate' is the definition.
(thesaurus)
'detective with charge' is the wordplay.
'detective' becomes 'pi' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'charge' becomes 'rate' (rate is a kind of charge**).
'pi'+'rate'='PIRATE'
'that's' is the link.
(Other definitions for pirate that I've seen before include "Bandit of the ocean, buccaneer" , "sailor" , "Use (another's work) for profit without permission" , "Hook for one" , "Teach, perhaps" .)