Sharing a common culture (6)
I believe the answer is:
ethnic
'sharing a common culture' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ethnic that I've seen before include "To do with racial group or culture" , "from a particular community" , "Indigenous" , "Of a way of living by a distinctive group" , "Relating to races" .)