spiritualism has 3 distinct synonyms spread across 1 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
(theology) any doctrine that asserts the separate existence of God
the belief that the spirits of dead people can communicate with people who are still alive (especially via a medium)
concern with things of the spirit
Synonyms, antonyms and the broader and narrower relations for spiritualism come from Princeton University’s WordNet. Full sources and licences.