The edge of night (4)
I believe the answer is:
dusk
'the edge of night' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dusk that I've seen before include "Eventide" , "The darker stage of twilight" , "Time of day after sunset" , "Sundown" , "Time between twilight and night" .)