Pageant topper (5)
I believe the answer is:
tiara
'pageant topper' 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 "High diadem" , "Ornamental headpiece" , "It might go to one's head" , "Ornamental head band" , "Jewelled hair-band" .)