Sully, besmirch (6)
I believe the answer is:
defile
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">sully</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that sully can be written as defile)</span><br/ ><br/ >'<span class="explanation-format__original">besmirch</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for defile that I've seen before include "Make dirty in narrow gorge" , "Contaminate" , "Befoul" , "Narrow pass; pollute" , "Soil" .)