Lorelei's river (5)
I believe the answer is:
rhine
'lorelei's river' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rhine that I've seen before include "Major European river" , "Great German river with Lorelei Rock" , "Bonn's river" , "Great river in Germany with Lorelei Rock" , "River flowing from Switzerland, through Germany, to the North Sea" .)