What is the meaning of -ness?

Appended to adjectives to form nouns meaning "the state of being (the adjective)", "the quality of being (the adjective)", or "the measure of being (the adjective)".

Appended to words of other parts of speech to form nouns (often nonce words or terms in philosophy) meaning the state/quality/measure of the idea represented by these words.

alternative form of -nesse

alternative form of -nes

Affixed to adjectives to form abstract nouns which denote a quality, state or condition.

Source: wiktionary.org