Light weight (5)
I believe the answer is:
ounce
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">light weight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ounce that I've seen before include "Unit of weight - snow leopard" , "Small amount (of old pound)" , "one of sixteen in a pound" , "not weighing very much" , "Oz" .)