brilliancy vs brilliant

brilliancy is a noun but brilliant is not a noun.

Word	Noun	Adjective	Verb	Adverb
brilliancy	Yes	No	No	No
brilliant	No	Yes	No	No

brilliancy (noun)	brilliant (noun)
a quality that outshines the usual

brilliancy (adjective)	brilliant (adjective)
	full of light; shining intensely
	having strong or striking color
	characterized by grandeur
	having or marked by unusual and impressive intelligence
	clear and sharp and ringing
	of surpassing excellence