Force; ferocity (8)
I believe the answer is:
violence
I believe this is a double definition.
'force' is the first definition.
(force can mean violence or aggression)
'ferocity' is the second definition.
(I know that ferocity can be written as violence)
(Other definitions for violence that I've seen before include "Unjustifiable force" , "Once evil (anag)" , "Harmful behaviour" , "Aggressive force" , "Force, injury" .)