Grave, serious (4)
I believe the answer is:
grim
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">grave</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">serious</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for grim that I've seen before include "Serious; dour" , "Stern, cruel" , "Severe; horrible" , "Dire" , "Dreadful" .)