Arsenic (6)
I believe the answer is:
poison
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">arsenic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for poison that I've seen before include "Meat for someone else" , "Corrupt" , "Deadly substance" , "Bane" , "Venom, harmful substance" .)