From aggressive + -ness.

• IPA^(key): /əˈɡrɛsɪvnɪs/

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aggressiveness (usually uncountable, plural aggressivenesses)

1. (uncountable) The state or quality of being aggressive.

   Synonyms: aggression, aggressivity

   • 1992, Toni Morrison, Jazz, Vintage (2016), page 29:

     It was a randy aggressiveness he had enjoyed because he had not used or needed it before.

2. (uncountable) The propensity of a soil or water to dissolve metal or cement structures.

   The aggressiveness of various sulfate salts towards concrete is partly related to solubility.

3. (countable) The result or product of being aggressive.