Expression of disapproval over universal ballet wear (4)
I believe the answer is:
tutu
'ballet wear' is the definition.
(I've seen this in another clue)
'expression of disapproval over universal' is the wordplay.
'expression of disapproval' becomes 'tut' (sound made to express disapproval).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'universal' becomes 'U' (film certificate).
'tut'+'u'='TUTU'
(Other definitions for tutu that I've seen before include "Female ballet costume" , "Short skirt for ballet dancer" , "Ballet dancer's costume" , "Ballet dancer's short skirt" , "Ballet dress" .)