Foolishness, inanity (9)
I believe the answer is:
asininity
I believe this is a double definition.
'foolishness' is the first definition.
(I know that asininity is a type of foolishness)
'inanity' is the second definition.
(thesaurus)
(Other definitions for asininity that I've seen before include "Stupidity" , "Extreme foolishness" , "Idiocy" , "Foolishness as of donkey" .)