Tarnish; dye (5)
I believe the answer is:
stain
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">tarnish</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that tarnish can be written as stain)</span><br/ ><br/ >'<span class="explanation-format__original">dye</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that stain is a type of dye)</span><br/ ><br/ ></span>
(Other definitions for stain that I've seen before include "Mark with colour, dirt" , "Discoloration" , "Blot" , "Discolouration" , "Discolouring mark" .)