region has 4 distinct synonyms spread across 4 of its 5 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.
Synonyms, antonyms and the broader and narrower relations for region come from Princeton University’s WordNet. Full sources and licences.
a part of an animal that has a special function or is supplied by a given artery or nerve
“in the abdominal region”
a large indefinite location on the surface of the Earth
“penguins inhabit the polar regions”
the approximate amount of something (usually used prepositionally as in `in the region of')
“it was going to take in the region of two or three months to finish the job”
a knowledge domain that you are interested in or are communicating about
“it was a limited realm of discourse”