Grave, solemn (7)
I believe the answer is:
serious
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">grave</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that grave can be written as serious)</span><br/ ><br/ >'<span class="explanation-format__original">solemn</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for serious that I've seen before include "Earnest; vital" , "Not light or frivolous" , "Stern" , "Important - solemn" , "Solemn, thoughtful" .)