One with corner on river? (6)
I believe the answer is:
angler
'one' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'corner on river?' is the wordplay.
I cannot quite see how this works, but
'corner' could be 'angle' (I've seen this in another clue) and 'angle' is found in the answer.
'river?' could be 'r' (abbreviation for river) and 'r' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'with' acts as a link.
(Other definitions for angler that I've seen before include "person hoping to catch fish" , "One proverbially exaggerating" , "I cast Rod" , "I may do casting" , "Sportsman" .)