英语词源字典 - 在线词源网站

brightness (n.)[brightness 词源字典]: Old English beorhtnes "brightness, clearness, splendor, beauty;" see bright + -ness.[brightness etymology, brightness origin, 英语词源]
clarity (n.): c. 1300, clarte "brightness," from Old French clarté "clarity, brightness," from Latin claritas "brightness, splendor," also, of sounds, "clearness;" figuratively "celebrity, renown, fame," from clarare "make clear," from clarus "clear" (see clear (adj.)). Modern form is early 15c., perhaps a reborrowing from Latin. Meaning "clearness" is from 1610s.
evidence (n.): c. 1300, "appearance from which inferences may be drawn," from Old French evidence, from Late Latin evidentia "proof," in classical Latin "distinction, vivid presentation, clearness" in rhetoric, from stem of Latin evidens "obvious, apparent" (see evident).

Meaning "ground for belief" is from late 14c.; that of "obviousness" is from 1660s and tacks closely to the sense of evident. Legal senses are from c. 1500, when it began to oust witness. Also "one who furnishes testimony, witness" (1590s); hence turn (State's) evidence.
perspicuity (n.): late 15c., of things; 1540s, of expressions, from Latin perspicuitas "transparency, clearness," from perspicuus, from perspicere "look through, look closely at" (see perspective).
serenity (n.): 1530s, of weather, 1590s, of persons, from Middle French sérénité, from Latin serenitatem (nominative serenitas) "clearness, serenity," from serenus (see serene). Earliest use (mid-15c.) was as a title of honor for kings, probably from the similar use of Latin serenitas, applied to Roman emperors, later popes.