Bluish-white metal (4)
I believe the answer is:
zinc
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bluish-white metal</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 zinc that I've seen before include "Metallic element present with copper in brass" , "Metal alloyed with copper to make brass" , "White metallic element, symbol Zn" , "Type of metal" , "Anti-corrosion agent" .)