Skirt shape (4)
I believe the answer is:
hoop
'skirt shape' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hoop that I've seen before include "Metal ring for croquet and basketball" , "Circular band, in basketball, say" , "Arch used in croquet" , "round during dance" , "Ring of wood - arch at croquet" .)