Zn (4)
I believe the answer is:
zinc
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">zn</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for zinc that I've seen before include "Sivery-white metal" , "Ingredient in brass" , "Metallic element present with copper in brass" , "it might be galvanising" , "White metallic element, symbol Zn" .)