Irrationality (8)
I believe the answer is:
unreason
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">irrationality</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that irrationality can be written as unreason)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for unreason that I've seen before include "insanity" , "foolishness" , "Irrationality" , "nonsense" , "The absence of rationality or logic" .)