You heard expression of disapproval about short skirt (4)
I believe the answer is:
tutu
'short skirt' is the definition.
(I've seen this before)
'you heard expression of disapproval about' is the wordplay.
'you heard' becomes 'U' (homophone of 'you').
'expression of disapproval' becomes 'tut' (sound made to express disapproval).
'about' shows that the letters should be reversed in order.
'u'+'tut'='utut'
'utut' in reverse letter order is 'TUTU'.
(Other definitions for tutu that I've seen before include "Short dress" , "In which dancer may appear" , "Ballerina's stiff skirt" , "outfit" , "Ballet dancer's costume" .)