Stream of brilliance (4)
I believe the answer is:
rill
'stream' is the definition.
(I know that rill is a type of stream)
'of brilliance' is the wordplay.
'of' indicates the answer is hidden within the clue.
'RILL' can be found hidden inside 'brilliance'.
(Other definitions for rill that I've seen before include "Flowing water" , "Brooklet" , "Little stream" , "Burn" , "Small brook" .)