River’s end (5)
I believe the answer is:
delta
'river's end' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for delta that I've seen before include "sort of wing" , "Area of distributaries at a river mouth" , "Extended area at river mouth" , "Estuary area where river has split" , "The fourth Greek letter found at river's mouth" .)