Diamond figure (5)
I believe the answer is:
carat
'diamond figure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for carat that I've seen before include "Unit of weight for gems or purity of gold" , "Not a large weight" , "Unit of weight for gems and pearls" , "Unit for precious stone weights" , "Measure of fineness of gold" .)