Most furious (8)
I believe the answer is:
angriest
'most furious' is the definition.
('angry' can be a synonym of 'furious')
This is all the clue.
(Other definitions for angriest that I've seen before include "Most annoyed or hostile" , "Most irate and furious" , "Extremely mad" , "Most incensed kind of ingrates" , "Most characteristic of 1950s young men" .)