High IQ society (5)
I believe the answer is:
mensa
'high iq society' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mensa that I've seen before include "High-IQ society" , "High IQ society" , "IQ-based organisation" , "Organisation for people with high IQ" , "Organisation for those with high IQs" .)