Bit of sunlight (3)
I believe the answer is:
ray
'bit of sunlight' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ray that I've seen before include "Flat fish or sun beam" , "A bright beam or flat fish" , "bit of sunshine" , "Beam or flatfish" , "Broad flat fish; beam" .)