"quality of being brilliant," 1747; see brilliant + abstract noun suffix -cy. Also compare brilliance.
Entries linking to brilliancy
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).
The 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.
-cy
abstract noun suffix of quality or rank, from Latin -cia, -tia, from Greek -kia, -tia, from abstract ending -ia (see -ia) + stem ending -c- or -t-. The native correspondents are -ship, -hood.
brilliance n.
"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.