Shiny metal (6)
I believe the answer is:
chrome
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shiny 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 chrome that I've seen before include "A yellow colouring matter" , "Decorative plating" , "Shiny metal for plating" , "Protective finish on motor vehicle fittings" , "Feature of bath taps" .)