River no longer noted? (3)
I believe the answer is:
exe
'river' is the definition.
(River Exe)
'no longer noted?' is the wordplay.
I cannot really see how this works, but
'no longer' could be 'ex' (prefix meaning former or onetime) and 'ex' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for exe that I've seen before include "Somerset/Devon river" , "Runner" , "River in SW UK" , "Tiverton's river" , "River of southwest England" .)