Mindlessness (7)
I believe the answer is:
'mindlessness' is the definition.
(I know that mindlessness can be written as inanity)
This is all the clue.
(Other definitions for inanity that I've seen before include "Being silly" , "Puerility" , "Silliness in a tiny way" , "Foolishness" , "Folly" .)