from The American Heritage® Dictionary of the English Language, 4th Edition
- suffix State; quality; condition; degree: brightness.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- suffix Appended to adjectives to form nouns meaning "the state of (the adjective)", "the quality of (the adjective)", or "the measure of (the adjective)".
- suffix 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.
from the GNU version of the Collaborative International Dictionary of English
- A suffix used to form abstract nouns expressive of quality or state.
Middle English -nes, from Old English.(American Heritage® Dictionary of the English Language, Fourth Edition)
Middle English, from Old English -nis, -nes ("-ness"), from Proto-Germanic *-nassuz (“-ness”), alteration (by false division) of -n- (adjective and verbal terminating consonant) + Proto-Germanic *-assuz (“-ness”). Akin to Old Saxon -nissi, -nussi (Dutch -nis), Old High German -nissa, -nassi, -nussi (German -nis), Gothic -inasus, -inassus (Wiktionary)