forbidden city has 3 distinct synonyms spread across 1 of its 2 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 sacred city of Lamaism; known as the Forbidden City for its former inaccessibility and hostility to strangers
a walled section of Beijing that encloses the palace that was formerly the residence of the emperor of China
Synonyms, antonyms and the broader and narrower relations for forbidden city come from Princeton University’s WordNet. Full sources and licences.