noun
Refers to the trait or quality of being aggressive, often used in psychological, behavioral, or descriptive contexts.
彼の攻撃性が問題になっている。
His aggressiveness has become a problem.
この犬種は攻撃性が低
This dog breed is said to have low aggression.
積極性 means 'proactiveness' or 'assertiveness' in a positive sense, whereas 攻撃性 often carries a negative or hostile connotation.
Compound of 攻撃 (attack) + 性 (nature, -ness). The derivation is straightforward from its components.