Not to be endured (11)
I believe the answer is:
intolerable
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not to be endured</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 intolerable that I've seen before include "Unable to be endured" , "Unbearable" , "The last straw" .)