Origin: 1675–85; < Frenchbrillant shining, present participle of briller < Italianbrillare to glitter (perhaps derivative of an expressive root); see -ant
1680s, from Fr. brilliant "sparkling, shining" prp. of briller "to shine" (16c.), from It. brillare "sparkle, whirl," perhaps from V.L. *berillare "to shine like a beryl," from berillus "beryl, precious stone," from L. beryllus (see beryl). In reference to diamonds (1680s)
it means a flat-topped cut invented 17c. by Venetian cutter Vincenzo Peruzzi.