Assertive personality (4,1)
I believe the answer is:
type a
'assertive personality' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for type a that I've seen before include "full of ambition and energy" , "what online solvers would do at 15" , "stress-inducing nature" , "ambitious sort" , "Strong personality" .)