WordNet records no synonym and no antonym for spanish inquisition. 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.
an inquisition initiated in 1478 by King Ferdinand and Queen Isabella that guarded the orthodoxy of Catholicism in Spain (especially from the 15th to the 17th centuries)
“the Spanish Inquisition was administered by both civil and church authorities which gave it ultimate power”
Synonyms, antonyms and the broader and narrower relations for spanish inquisition come from Princeton University’s WordNet. Full sources and licences.