Make dirty (4)
I believe the answer is:
soil
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">make dirty</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for soil that I've seen before include "Earth; make dirty" , "Dirty - dirt" , "Earth for growing" , "Top layer of the surface of the earth" , "Earth; stain" .)