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
). In reference to diamonds (1680s) it means a flat-topped cut invented 17c. by Venetian cutter Vincenzo Peruzzi.