Silvery-white metallic element (9)
I believe the answer is:
potassium
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">silvery-white metallic element</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for potassium that I've seen before include "Soft metal, symbol K" , "Soft metallic element" , "Soft reactive metal" , "Silvery metallic element" , "... is its atomic number: symbol K" .)