Legendary Rhine siren (7)
I believe the answer is:
lorelei
'legendary rhine siren' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lorelei that I've seen before include "High rock in the Rhine gorge" , "Rhine Rock where siren lived" , "alluring female" , "Fatal attraction" , "Great Rock on the Rhine where sirens lived in legend" .)