Dee river in evening light (4)
I believe the answer is:
dusk
'evening light' is the definition.
(I've seen this before)
'dee river' is the wordplay.
'dee' becomes 'd'.
'river' becomes 'usk' (Welsh river).
'd'+'usk'='DUSK'
'in' acts as a link.
(Other definitions for dusk that I've seen before include "Time between twilight and night" , "The darker stage of twilight" , "Nightfall" , "Evening light" , "Period after sunset" .)