Antonyms: dull, lackluster, obscure, dim, opaque, murky, nebulous, dingy, tarnished, sullied. brighten, v. polish, burnish, furbish; illuminate, irradiate, cheer, rally, enliven, inspirit. brightness, n. brilliancy, splendor, luster, luminosity, resplendence, radiance, refulgence, effulgence, glow; aptness, precocity, acuteness, sharpness, discernment; vivacity, animation, liveliness. brilliancy, n. brightness, resplendence, refulgence, brilliance.