"Swan Lake" attire (4)
I believe the answer is:
tutu
'swan lake attire' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tutu that I've seen before include "Female ballet costume" , "Ballerina's costume" , "In which dancer may appear" , "Ballet-dancer's skirt" , "Ballerina's stiff skirt" .)