Princess's headgear (5)
I believe the answer is:
tiara
'princess's headgear' 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 crown" , "it goes to one's head!" , "Half a crown!" , "Small crown" , "Woman's headdress for very formal occasions" .)