Open sore (5)
I believe the answer is:
ulcer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">open sore</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 ulcer that I've seen before include "Cruel kind of open sore" , "Sore point" , "Continuing source of pain" , "Cruel (anag.)" , "cause of suffering" .)