Stained; very dark (4)
I believe the answer is:
inky
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">stained</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">very dark</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(inky black)</span><br/ ><br/ ></span>
(Other definitions for inky that I've seen before include "Dark; stained" , "Leaked on by pen" , "Jet" , "Coloured black" , "Like the printing trade" .)