Pageant headpiece (5)
I believe the answer is:
tiara
'pageant headpiece' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tiara that I've seen before include "Top decoration" , "Jewelled head band" , "Jewelled head wear" , "Jewelled headwear" , "Jewelled hair-band" .)