German siren from tradition that is left over (7)
I believe the answer is:
lorelei
'german siren' is the definition.
(siren in German folklore)
'tradition that is left over' is the wordplay.
'tradition' becomes 'lore' (I've seen this in another clue).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'left' becomes 'l' (common abbreviation).
'over' says the letters should be written backwards.
'ie'+'l'='iel'
'iel' backwards is 'lei'.
'lore'+'lei'='LORELEI'
'from' is the link.
(Other definitions for lorelei that I've seen before include "voice to die for" , "Rock-dwelling siren" , "Great Rock on the Rhine where 37 across lived" , "Jerk" , "Dangerous female" .)