Difficult, tough (4)
I believe the answer is:
hard
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">difficult</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that difficult can be written as hard)</span><br/ ><br/ >'<span class="explanation-format__original">tough</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that tough can be written as hard)</span><br/ ><br/ ></span>
(Other definitions for hard that I've seen before include "Novel featuring Mr Gradgrind" , "Unyielding" , "Firm; demanding; stern" , "Tough; rigid" , "Difficult; rigid" .)