Disown bombast that goes around the City (6)
I believe the answer is:
recant
'disown' is the definition.
(thesaurus)
'bombast that goes around the city' is the wordplay.
'bombast' becomes 'rant' ('rant' can be a synonym of 'bombast').
'that goes around' is an insertion indicator.
'the city' becomes 'ec' (the City of London postcode).
'rant' enclosing 'ec' is 'RECANT'.
(Other definitions for recant that I've seen before include "Renounce (a heretical belief)" , "Revoke a former declaration" , "Renounce a former opinion or belief" , "Disavow" , "Take back something said" .)