Foolish, brainless (7)
I believe the answer is:
asinine
I believe this clue is a double definition.
'foolish' is the first definition.
(similar in meaning)
'brainless' is the second definition.
(I've seen this in another clue)
(Other definitions for asinine that I've seen before include "Stupid (as a donkey?)" , "Foolish, silly" , "Donkey-like" , "Jenny's often like this" , "Absurd" .)