Strict or stern (6)
I believe the answer is:
severe
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">strict</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">stern</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for severe that I've seen before include "'Strict, harsh (6)'" , "Very plain in style or appearance" , "Harsh and punitive" , "Austere, grim" , "Austere or strict" .)