Sore; corrupting influence (5)
I believe the answer is:
ulcer
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">sore</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">corrupting influence</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(ulcer can mean a moral blemish)</span><br/ ><br/ ></span>
(Other definitions for ulcer that I've seen before include "Cruel kind of open sore" , "Inflamed lesion" , "Spot of bother" , "Continuing source of pain" , "Cruel kind of bodily sore" .)