Tiara sparkler (3)
I believe the answer is:
gem
'tiara sparkler' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gem that I've seen before include "Treasured person" , "Setter might bed this" , "Half of 7 [SIGN OF THE ZODIAC]" , "Precious or semi-precious stone" , "Emerald or sapphire, say" .)