One way you could begin to characterise ‘aggressive’? (4,1)
I believe the answer is:
type a
''aggressive'?' is the definition.
(a type A personality is aggressive and competitive)
I don't understand the rest of the clue.
(Other definitions for type a that I've seen before include "Strong personality" , "stress-inducing nature" , "full of ambition and energy" , "ambitious sort" , "what online solvers would do at 15" .)