Mass murder (7)
I believe the answer is:
carnage
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mass murder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for carnage that I've seen before include "Wholesale killing" , "Wholesale slaughter" , "destruction" , "Mass killing" , "Mass slaughter" .)