Nagging pain (4)
I believe the answer is:
ache
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nagging pain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ache that I've seen before include "Throb - hurt" , "anguish" , "painful" , "Feel pain" , "suffering" .)