bril·liant / ˈbrilyənt/ • adj. 1. (of light) very bright and radiant. ∎  (of a color) brightly and intensely vivid.2. exceptionally clever or talented: a brilliant young mathematician a brilliant idea. ∎  outstanding; impressive: his brilliant career at Harvard. ∎ Brit., inf. very good, excellent, or marvelous: we had a brilliant time.• n. a diamond of brilliant cut.DERIVATIVES: bril·liant·ly adv.

brilliant XVII (not frequent before XVIII). — F. brillant, prp. of briller shine — It. brillare, of unkn. orig. See BERYL.