Inane, fatuous (7)
I believe the answer is:
asinine
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">inane</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">fatuous</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(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" .)