WordNet records no synonym and no antonym for inquisition. It is the only member of each of its synsets, 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 former tribunal of the Roman Catholic Church (1232-1820) created to discover and suppress heresy
a severe interrogation (often violating the rights or privacy of individuals)
Synonyms, antonyms and the broader and narrower relations for inquisition come from Princeton University’s WordNet. Full sources and licences.