brilliant (adj.)

hard, lustrous mineral occurring in hexagonal prisms, c. 1300, from Old French beryl (12c., Modern French béryl), from Latin beryllus, from Greek bēryllos, which is perhaps from Prakrit veruliya, from Sanskrit vaidurya-, of Dravidian origin, which might be from the city of Velur (modern Belur) in southern India.

In Medieval Latin berillus was applied to any precious stone of a pale green color, to fine crystal, and to eyeglasses (the first spectacle lenses may have been made of beryl), hence German Brille "spectacles," from Middle High German berille "beryl," and French besicles (plural) "spectacles," altered 14c. from Old French bericle.

"quality of being brilliant," 1755, from brilliant + -ance. The figurative sense (of wit, intelligence, etc.) is from 1779. Distinguished from brilliancy in that the latter usually is applied to things measurable in degrees.

"quality of being brilliant," 1747; see brilliant + abstract noun suffix -cy. Also compare brilliance.