The Collaborative International Dictionary of English v.0.48:

Brillancy \Bril"lan*cy\, n. [See Brilliant.]
   The quality of being brilliant; splendor; glitter; great
   brightness, whether in a literal or figurative sense.
   [1913 Webster]

         With many readers brilliancy of style passes for
         affluence of thought.                    --Longfellow.
   [1913 Webster]