Gentle illumination (5)
I believe the answer is:
light
This clue is a double definition.
'gentle' is the first definition.
(synonyms)
'illumination' is the second definition.
(I know that light is a type of illumination)
(Other definitions for light that I've seen before include "Opposite of dark" , "weighing relatively little" , "Whitish" , "answer to clue" , "free gift from The Sun" .)