Jewelled head ornament (5)
I believe the answer is:
tiara
'jewelled head ornament' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tiara that I've seen before include "Top decoration" , "Crescent-shaped headdrsss or Pope's diadem" , "Jewelled headband" , "Type of diadem" , "Jewelled head wear" .)