Inane, fatuous (7)
I believe the answer is:
asinine
I believe this clue is a double definition.
'inane' is the first definition.
(synonyms)
'fatuous' is the second definition.
(synonyms)
(Other definitions for asinine that I've seen before include "In the nature of supposedly stupid animal" , "Stubborn" , "'Mindless, vacuous (7)'" , "Senseless" , "Silly like a donkey" .)