Deep-seated; persistent (7)
I believe the answer is:
chronic
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">deep-seated</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">persistent</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(a chronic condition is a persistent one)</span><br/ ><br/ ></span>
(Other definitions for chronic that I've seen before include "pants" , "(Of illness) lengthy; very bad (colloq.)" , "Of illness, prolonged or constantly recurring" , "Very serious" , "Not acute" .)