Unit of gem weight (5)
I believe the answer is:
carat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unit of gem weight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for carat that I've seen before include "Unit of weight used for gems" , "Gem weight unit" , "Diamond weight unit" , "Not a large weight" , "Precious stone weight" .)