Students of French enthralled by derrières (7)
I believe the answer is:
readers
'students' is the definition.
(reader is a kind of student)
'of french enthralled by derrieres' is the wordplay.
'of french' becomes 'de' ('of' in French).
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'derrieres' becomes 'rears' ('rear' can be a synonym of 'derriere').
'de' inserted into 'rears' is 'READERS'.
(Other definitions for readers that I've seen before include "Senior lecturers" , "cheaters" , "Lectors" , "bookworms" , "Student textbooks" .)