southwest has 8 distinct synonyms spread across 5 of its 7 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.
the compass point midway between south and west; at 225 degrees
the southwestern region of the United States generally including New Mexico, Arizona, Texas, California, and sometimes Utah and Colorado
the direction corresponding to the southwestward compass point
a location in the southwestern part of a country, region, or city
situated in or oriented toward the southwest
to, toward, or in the southwest
Synonyms, antonyms and the broader and narrower relations for southwest come from Princeton University’s WordNet. Full sources and licences.