Pageant winner's headpiece (5)
I believe the answer is:
tiara
'pageant winner's headpiece' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tiara that I've seen before include "Ornamental head gear" , "special headgear" , "Decorative headband" , "Jewelled hair-band" , "Half a crown!" .)