Ness nemesis (6)
I believe the answer is:
capone
'ness nemesis' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for capone that I've seen before include "US gangster (St Valentine's Day massacre)" , "Mountain said to be resting place of Noah's Ark" , "Al - , notorious gangster" , "Notorious criminal" , "Italian-American gangster, d. 1947" .)