WordNet records no synonym and no antonym for received pronunciation. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the approved pronunciation of British English; originally based on the King's English as spoken at public schools and at Oxford and Cambridge Universities (and widely accepted elsewhere in Britain); until recently it was the pronunciation of English used in British broadcasting
Synonyms, antonyms and the broader and narrower relations for received pronunciation come from Princeton University’s WordNet. Full sources and licences.