Dull, gloomy (7)
I believe the answer is:
subfusc
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">dull</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">gloomy</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for subfusc that I've seen before include "dress for Zuleika Dobson?" , "Dull, gloomy; academic dress" , "Formal university wear" , "Surprisingly dull" , "Dull in colour" .)