-ness

Appended in general, often informally, stylistically, or jocularly, for reification of an attribute.

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.