Brainlessness is a related term of fatuousness.
As nouns the difference between brainlessness and fatuousness
is that brainlessness is the state or condition of being brainless while fatuousness is the characteristic of being fatuous.
brainlessness
English
Noun
(-)
The state or condition of being brainless.
fatuousness
English
Noun
(en-noun)
The characteristic of being fatuous.