Foolishness, stupidity (6)
I believe the answer is:
idiocy
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">foolishness</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">stupidity</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(idiocy is a kind of stupidity)</span><br/ ><br/ ></span>
(Other definitions for idiocy that I've seen before include "Stupid behaviour or talk" , "Imbecility" , "Chopper" , "Extreme silliness" , "Complete folly" .)