Capone’s nemesis (4)
I believe the answer is:
ness
'capone's nemesis' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ness that I've seen before include "Scottish Lough containing legendary monster" , "Scottish Loch with legendary monster" , "Headland, promontory" , "Headland, cape" , "Scottish loch - headland" .)