The quality of being brilliant; extreme brightness, intelligence, or outstanding excellence in performance.
From 'brilliant' plus the noun suffix '-cy,' forming an abstract quality noun. 'Brilliant' itself comes from Latin 'berillus,' a shining gemstone.
Brilliancy was a favorite word of Victorian writers and critics—they loved using it to describe both literally shining things (diamonds, candlelight) and figuratively brilliant minds, as if intelligence literally radiated light.
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