WordNet records no synonym and no antonym for ecclesiastical province. 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 district within the jurisdiction of an archbishop or a metropolitan or one of the territorial divisions of an ecclesiastical order
“the general of the Jesuits has several provinces under him”
Synonyms, antonyms and the broader and narrower relations for ecclesiastical province come from Princeton University’s WordNet. Full sources and licences.