WordNet records no synonym and no antonym for subdeacon. 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 clergyman an order below deacon; one of the Holy Orders in the unreformed western Christian church and the eastern Catholic Churches but now suppressed in the Roman Catholic Church
Synonyms, antonyms and the broader and narrower relations for subdeacon come from Princeton University’s WordNet. Full sources and licences.