Use gin to develop brilliance (6)
I believe the answer is:
genius
'brilliance' is the definition.
(I know that brilliance can be written as genius)
'use gin to develop' is the wordplay.
'to develop' indicates an anagram.
'use'+'gin'='usegin'
'usegin' with letters rearranged gives 'GENIUS'.
(Other definitions for genius that I've seen before include "Brilliance" , "Person of exceptional mental ability" , "Virtuoso" , "no dope" , "Exceptional intellect" .)