Holocaust (8)
I believe the answer is:
genocide
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">holocaust</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for genocide that I've seen before include "Ethnic cleansing" , "Extermination of ethnic group or nationality" , "Racial murder" , "Deliberate extermination of a race of people" , "Large-scale killing" .)