Tend to course around Seine's banks (5)
I believe the answer is:
nurse
'tend to' is the definition.
(I've seen this before)
'course around seine's banks' is the wordplay.
'course' becomes 'run' (synonyms).
'around' says the letters should be written backwards.
'banks' suggests removing the centre (the sides or banks of the word).
'seine' with its centre removed is 'se'.
'run' backwards is 'nur'.
'nur'+'se'='NURSE'
(Other definitions for nurse that I've seen before include "Runes (anag)" , "Minister to" , "Angel of mercy" , "Care for - harbour" , "Look after the sick" .)