WordNet records no synonym and no antonym for pointillism. 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 school of painters who used a technique of painting with tiny dots of pure colors that would blend in the viewer's eye; developed by Georges Seurat and his followers late in 19th century France
a genre of painting characterized by the application of paint in dots and small strokes; developed by Georges Seurat and his followers in late 19th century France
Synonyms, antonyms and the broader and narrower relations for pointillism come from Princeton University’s WordNet. Full sources and licences.