Eg, iron or copper (5)
I believe the answer is:
metal
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">eg iron</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that Fe is a type of metal)</span><br/ ><br/ >'<span class="explanation-format__original">copper</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for metal that I've seen before include "Silver or gold, say" , "Musically it can be heavy" , "Like steel cutlery" , "Copper possibly" , "Eg, copper" .)