Ballerinas' skirts (5)
I believe the answer is:
tutus
'ballerinas' skirts' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tutus that I've seen before include "Ballet costumes" , "Ballet skirts" , "Certain dance outfits" , "Ballerinas' short skirts" , "Ballet dresses" .)