Very strict (6)
I believe the answer is:
severe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">very strict</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for severe that I've seen before include "Harsh and punitive" , "Extreme - strict" , "Strict, hard" , "'Strict, harsh (6)'" , "Harsh - extreme" .)