"To Kill a Mockingbird" theme (6)
I believe the answer is:
racism
'to kill a mockingbird theme' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for racism that I've seen before include "A basis for hate crime" , "Ethnic discrimination" , "Prejudice against another people" , "Prejudice against people of different origin" , "Nazi-style discrimination" .)