Dull pain (4)
I believe the answer is:
ache
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dull pain</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 ache that I've seen before include "Feel sore" , "Longing" , "Similar" , "A dull lingering pain" , "strong feeling" .)