southern has 1 distinct synonym spread across 2 of its 4 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. Its one recorded opposite is northern.
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.
in or characteristic of a region of the United States south of (approximately) the Mason-Dixon line
“southern hospitality”
situated in or coming from regions of the south
“the southern hemisphere”
Synonyms, antonyms and the broader and narrower relations for southern come from Princeton University’s WordNet. Full sources and licences.