WordNet records no synonym and no antonym for private practice. 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.
the practice of a profession independently and not as an employee
“he teaches at the medical school but his fortune came from private practice”
Synonyms, antonyms and the broader and narrower relations for private practice come from Princeton University’s WordNet. Full sources and licences.