Metric weight unit (4)
I believe the answer is:
gram
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">metric weight unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(gram is a kind of metric weight unit)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for gram that I've seen before include "Small unit of mass" , "Metric unit of mass" , "pulses" , "Metric unit of weight" , "Chickpeas; unit of mass" .)