Intractable (9)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">intractable</span>' is the definition.<br/ ><span class="explanation-format__explanation">(associated in meaning)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for obstinate that I've seen before include "Firm" , "Like mules" , "Stubbornly persistent" , "Inflexible" , "Cussed" .)
(Other definitions for difficult that I've seen before include "Requiring much effort" , "Hard, not easy" , "Demanding" , "Challenging" , "Trying" .)