WordNet records no synonym and no antonym for arches national park. 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.
a national park in Utah including mountains and the Colorado River gorge and huge rock formations caused by erosion
Synonyms, antonyms and the broader and narrower relations for arches national park come from Princeton University’s WordNet. Full sources and licences.