Exacting (5)
I believe the answer is:
stern
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">exacting</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that exacting can be written as stern)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for stern that I've seen before include "Inflexible; back" , "Unsmiling" , "Severe, demanding" , "discipline" , "Severe, forbidding" .)