Damage or spoil (3)
I believe the answer is:
mar
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">damage</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(to mar is to spoil or damage)</span><br/ ><br/ >'<span class="explanation-format__original">spoil</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for mar that I've seen before include "Spoil something" , "A windy month" , "Make imperfect" , "Ruin" , "wreck" .)