Deep narrow gorge (6)
I believe the answer is:
ravine
'deep narrow gorge' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ravine that I've seen before include "Deep narrow gorge with steep sides" , "'Deep, steep valley (6)'" , "Narrow, steep-sided valley" , "Vainer in narrow gorge" , "Deep narrow valley" .)