Inveterate criminal has business with my boss (9)
I believe the answer is:
confirmed
'inveterate' is the definition.
(thesaurus)
'criminal has business with my boss' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'has' means one lot of letters go next to another.
'business' becomes 'firm' (firm is a kind of business).
'with' means one lot of letters go next to another.
'my boss' becomes 'ed' (abbreviation for editor, the setter's boss).
'con'+'firm'+'ed'='CONFIRMED'
(Other definitions for confirmed that I've seen before include "Verified" , "Stated with assurance that something was true" .)