Obstacle, difficulty (6)
I believe the answer is:
hurdle
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">obstacle</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that hurdle is a type of obstacle)</span><br/ ><br/ >'<span class="explanation-format__original">difficulty</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that hurdle is a type of obstruction)</span><br/ ><br/ ></span>
(Other definitions for hurdle that I've seen before include "Barrier (to be jumped)" , "Light movable barrier in certain races" , "Problem to overcome" , "Obstacle used in races" , "Vault" .)