Fierceness (8)
I believe the answer is:
ferocity
'fierceness' is the definition.
(I know that fierceness can be written as ferocity)
This is the entire clue.
(Other definitions for ferocity that I've seen before include "Unrestrained and cruel savagery" , "State of savagery and violence" , "Wild savagery" , "Savage cruelty of temperament" , "Savageness" .)