Soot (5)
I believe the answer is:
grime
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">soot</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for grime that I've seen before include "an ingrained phenomenon" , "Dirt, grease" , "Filth, dirt" , "Muck" , "Engrained dirt" .)