Doctor and a copper taking on the French vampire (7)
I believe the answer is:
dracula
'vampire' is the definition.
(I've seen this before)
'doctor and a copper taking on the french' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor'**).
'and' means one lot of letters go next to another.
'copper' becomes 'cu' (chemical symbol).
'taking on' means one lot of letters go next to another.
'the french' becomes 'la'.
'dr'+'a'+'cu'+'la'='DRACULA'
(Other definitions for dracula that I've seen before include "Stoker's Count" , "Famous vampire" , "Bram Stoker creation" , "Bram Stoker's batman" , "Blood Count?" .)