WordNet records no synonym and no antonym for nullarbor plain. 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 vast arid plain of southern Australia stretching inland from the Great Australian Bight; has sparse vegetation and no surface water and is almost uninhabited; the site of a major rocket research center
Synonyms, antonyms and the broader and narrower relations for nullarbor plain come from Princeton University’s WordNet. Full sources and licences.