Unforgiving (9)
I believe the answer is:
merciless
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unforgiving</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for merciless that I've seen before include "Uncharitable" , "Totally unforgiving" , "Cruel" , "Showing no compassion" , "Ruthless" .)