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Webster 1828 Edition

Noun.

[See Brilliant.] Splendor; glitter; great brightness.

brilliancy ‎(countable and uncountable, plural brilliancies)

a shining quality; brilliance.
An act of being brilliant.
His brilliancy lay in combining old ideas from far flung fields into a new idea.‎
(chess) A spectacular and beautiful game of chess, generally featuring sacrificial attacks and unexpected moves.

shining quality

act of being brilliant