Pope's triple crown (5)
I believe the answer is:
tiara
'pope's triple crown' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tiara that I've seen before include "Half-crown?" , "Decorative headgear" , "Decorative headband" , "special headgear" , "Crescent-shaped headdrsss or Pope's diadem" .)