Serious in intention (7)
I believe the answer is:
earnest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">serious in intention</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for earnest that I've seen before include "Grave" , "Serious, intent" , "Fixed" , "Pledge - far from frivolous" , "Art deserving" .)