Merriam-Webster's Collegiate® Dictionary, 11th Edition
BRILLIANT
I. adjective
Etymology: French brillant, present participle of briller to shine, from Italian brillare
Date: 1696
very bright ; glittering ,
2. striking , distinctive , distinguished by unusual mental keenness or alertness, see: bright brilliantly adverb
II. noun
Date: 1690
a gem (as a diamond) cut in a particular form with numerous facets so as to have special brilliance