Metal mixture (5)
I believe the answer is:
alloy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">metal mixture</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 alloy that I've seen before include "Bronze or brass, perhaps" , "Metal mixture" , "Mixture of two or more metals" , "Eg, pewter or brass" , "Eg brass or bronze" .)