WordNet records no synonym and no antonym for defender of the faith. 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.
a title that Leo X bestowed on Henry VIII and later withdrew; parliament restored the title and it has been used by English sovereigns ever since
Synonyms, antonyms and the broader and narrower relations for defender of the faith come from Princeton University’s WordNet. Full sources and licences.