Major European river (5)
(Other definitions for rhone that I've seen before include "French river from Alps to Mediterranean" , "River flowing from Alps to the French Med" , "River at Avignon and Arles" , "Camargue river" , "Swiss-French river" .)
'major european river' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rhine that I've seen before include "River flowing from Switzerland, through Germany, to the North Sea" , "water" , "Great river in Germany with Lorelei Rock" , "Cologne's river" , "fed by 8 [RHUR]" .)