Shaft of sunlight (3)
I believe the answer is:
ray
'shaft 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 "bit of sunshine" , "Flatfish or sunbeam" , "Beam or flatfish" , "Second note for the flat fish" , "Shaft, beam" .)