Consider the following English sentence:
Clark Kent is the alter ego of Superman
The latter uses a Latin expression, alter ego, meaning the "other self".
Now, consider this sentence:
Jeffersonian Democracy is the antithesis of British political system
I am looking for a Latin word or short phrase that replaces "antithesis" in the latter sentence (I want to use Latin to give "force" to the expression). At the moment have found contrarius and adversus ego. Apparently, "anti" is not used in Latin (see related question) so "anti ego" might not be an option.