Central part in country isn't upper class — it’s the opposite (8)
I believe the answer is:
contrary
'it's the opposite' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for contrary that I've seen before include "Exact opposition" , "Opposed or perverse" , "At variance; awkward" , "Carry out (command)" , "Opposite, perverse" .)