Vocalist the French turn to (4)
I believe the answer is:
alto
'vocalist' is the definition.
(alto is a kind of vocalist)
'the french turn to' is the wordplay.
'the french' becomes 'la'.
'turn' says the letters should be written backwards.
'la' written backwards gives 'al'.
'al'+'to'='ALTO'
(Other definitions for alto that I've seen before include "Member of choir" , "Singing voice between tenor and soprano" , "Male singer" , "One who sings" , "A singing voice or pitch" .)