Official account believed (10)
I believe the answer is:
accredited
'official' is the definition.
(thesaurus)
'account believed' is the wordplay.
'account' becomes 'ac' (abbreviation for account).
'believed' becomes 'credited' (I've seen this before).
'ac'+'credited'='ACCREDITED'
(Other definitions for accredited that I've seen before include "Certified officially" , "Given official authorisation" , "Broadcast" , "Given official recognition" .)