unrelenting (10)
I believe the answer is:
persistent
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unrelenting</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for persistent that I've seen before include "fixed" , "Tenacious; constant" , "hanging on" , "not giving up" , "Not taking "no" for an answer" .)