Brilliant
late 17th century: from French brillant ‘shining’, present participle of briller, from Italian brillare, probably from Latin beryllus (see beryl).
wiktionary
Borrowed from French brillant (late 17th century), present participle of the verb briller, from Italian brillare, possibly from Latin berillus, beryllus(“a beryl, gem, eyeglass”), from Ancient Greek βήρυλλος(bḗrullos, “beryl”).
etymonline
brilliant (adj.)
"sparkling with light or luster," 1680s, from French brilliant "sparkling, shining" present participle of briller "to shine" (16c.), from Italian brillare "sparkle, whirl," perhaps from Vulgar Latin *berillare "to shine like a beryl," from berillus "beryl, precious stone," from Latin beryllus (see beryl).
Figurative sense of "distinguished by admirable qualities" is from 1848. Of diamonds from 1680s in reference to a flat-topped cut invented 17c. by Venetian cutter Vincenzo Peruzzi. Related: Brilliantly; brilliantness.
