Furious at Rome’s conspiracy of silence (6)
I believe the answer is:
omerta
'conspiracy of silence' is the definition.
(I've seen this before)
'furious at rome's' is the wordplay.
'furious' indicates an anagram (I've seen this in other clues).
'at'+'rome'='atrome'
'atrome' is an anagram of 'OMERTA'.
(Other definitions for omerta that I've seen before include "Mafia code of silence, never inform" , "vow of silence" , "Mafia pledge of silence" , "conspiracy of silence" , "Mafia code of silence; at Rome (anag.)" .)