Silliness (7)
I believe the answer is:
inanity
'silliness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for inanity that I've seen before include "act of stupidity" , "Mindlessness" , "Silliness in a tiny way" , "Foolishness" , "Being silly" .)