Physical river cut (5)
I believe the answer is:
canal
This clue might be a double definition.
'physical river' is the first definition.
The answer and definition can be both natural objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'cut' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for canal that I've seen before include "Passage" , "Long, narrow strip of water" , "Aqueduct" , "Manmade flower" , "Man-made watercourse" .)