Pertaining to a certain culture (6)
I believe the answer is:
ethnic
'pertaining to a certain 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 race and its customs" , "Relating to groups with common customs" , "Realting to race or culture" , "Culturally-based" , "Relating to a particular racial group" .)