Ballet costume (4)
I believe the answer is:
tutu
'ballet costume' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tutu that I've seen before include "Ballet dancer's short skirt" , "very short garment" , "Ballerina's stiff skirt" , "South African archbishop, b. 1931" , "In which dancer may appear" .)