Defiantly aggressive (9)
I believe the answer is:
truculent
'defiantly aggressive' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for truculent that I've seen before include "Rude and aggressive" , "Defiant, rude" , "Quarrelsome" , "Aggressively defiant" , "Defiantly aggressive" .)