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