Gangster getting mean makes one suffer (5)
I believe the answer is:
allow
'one suffer' is the definition.
(thesaurus)
'gangster getting mean' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'getting' is a charade indicator (letters next to each other).
'mean' becomes 'low' (I've seen this before).
'al'+'low'='ALLOW'
'makes' acts as a link.
(Other definitions for allow that I've seen before include "OK" , "Licence" , "Sanction" , "Permit or concede" , "Permit or agree" .)