Brainy group (5)
I believe the answer is:
mensa
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brainy group</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mensa that I've seen before include "High-IQ society" , "High IQ_organisation" , "Organisation for those with high IQs" , "Stars" , "High IQ society" .)