Royal headpiece (5)
I believe the answer is:
tiara
'royal 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 "Pope's triple-tiered crown" , "pope may have been topped by one" , "Jewelled hair-band" , "High diadem" , "expensive headwear" .)