Nether world (4)
I believe the answer is:
hell
'nether world' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hell that I've seen before include "Abode of evil spirits" , "Unpleasant place" , "'The road to . . . . is paved with good intentions'" , "Place of suffering" , "Abode of the forces of evil" .)