Definition of -ness in English:

suffix

• 1(forming nouns chiefly from adjectives) denoting a state or condition.

  ‘liveliness’

  ‘sadness’

  1. 1.1(forming nouns chiefly from adjectives) an instance of a state or condition.
     ‘a kindness’

• 2(forming nouns chiefly from adjectives) something in a certain state.

  ‘wilderness’