Cut off river loop (5)
I believe the answer is:
oxbow
'cut off river loop' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for oxbow that I've seen before include "U-shaped curve in a stream" , "Neat collar" , "Cut off river loop" , "Lake formed by a bend in a river" , "State of panic or fear" .)