Crossword Genius

River, extremely rough one (5)

Ross

I believe the answer is:

rhone

'river' is the definition.
(Rhone River is an example)

'extremely rough one' is the wordplay.
'extremely' suggests removing the centre.
'rough' with its centre removed is 'rh'.
'rh'+'one'='RHONE'

(Other definitions for rhone that I've seen before include "River of Switzerland and France" , "River flowing through Lake Geneva" , "wherein runs rain in Arbroath" , "River running through the city of Arles" , "Major French river, rising in Switzerland" .)

I've seen this clue in The Times.
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