Social groups in traditional societies (6)
I believe the answer is:
tribes
'social groups in traditional societies' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tribes that I've seen before include "Groups of families in traditional societies" , "Clans" , "Groups of people related by blood" , "Racial groups living in communities headed by chiefs" , "Communities of primitive or nomadic groups" .)