Confuse idiot, rant in convention (9)
I believe the answer is:
tradition
'convention' is the definition.
(thesaurus)
'confuse idiot rant' is the wordplay.
'confuse' indicates anagramming the letters.
'idiot'+'rant'='idiotrant'
'idiotrant' is an anagram of 'TRADITION'.
'in' is the link.
(Other definitions for tradition that I've seen before include "customary behaviour" , "Established usage" , "old habit" , "Customs etc handed down" , "Long-established custom or belief" .)