Middle English brightnesse "brilliance, radiance," from Old English beorhtnes "brightness, clearness, splendor, beauty;" see bright + -ness.
Entries linking to brightness
bright adj.
"radiating or reflecting light," Old English bryht, metathesis of beorht "bright; splendid; clear-sounding; beautiful; divine," from Proto-Germanic *berhtaz "bright" (source also of Old Saxon berht, Old Norse bjartr, Old High German beraht, Gothic bairhts "bright"), from PIE root *bhereg- "to shine; bright, white." The meaning "quick-witted, having brilliant mental qualities" is from 1741.
The Germanic word was commonly used to form given names, and figures in the etymology of Robert, Albert, Bertha, Egbert, Gilbert, Herbert, Hubert, Lambert. In modern German it survives in names only (Albrecht, Ruprecht) and has been otherwise lost.
-ness
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).