Aggressiveness (5)
(Other definitions for aggro that I've seen before include "Yobbish violence" , "belligerent behaviour" , "Provocation (informal)" , "Hostile troublemaking" , "Violent disturbance" .)
(Other definitions for pushiness that I've seen before include "Self-assertion; ambition" , "Ambitious quality" .)
'aggressiveness' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for belligerence that I've seen before include "Aggressive behaviour" , "Aggressiveness" , "Pugnacity" , "Aggression" , "sabre-rattling" .)