Express disapproval with uniform dress (4)
I believe the answer is:
tutu
'dress' is the definition.
(I have seen 'Short dress' mean 'tutu' so perhaps 'dress' could also mean 'tutu')
'express disapproval with uniform' is the wordplay.
'express disapproval' becomes 'tut' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'tut'+'u'='TUTU'
(Other definitions for tutu that I've seen before include "Giselle's skirt" , "Archbishop Desmond" , "Ballet dancer's costume" , "In which dancer may appear" , "Ballet-dancer's skirt" .)