Treasure measure (5)
I believe the answer is:
carat
'treasure measure' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for carat that I've seen before include "Precious stone weight" , "Gemstone weight unit" , "Unit of weight for gems or purity of gold" , "Unit of weight of gemstones" , "Unit of weight for diamonds" .)