Big US gangster bringing death (5)
I believe the answer is:
fatal
'bringing death' is the definition.
(I've seen this before)
'big us gangster' is the wordplay.
'big' becomes 'fat'.
'us gangster' becomes 'al' (Al Capone).
'fat'+'al'='FATAL'
(Other definitions for fatal that I've seen before include "Involving death" , "Disastrous, maybe lethal" , "Causing death, say accident" , "Bringing ruin" , "making one late" .)