WordNet records no synonym and no antonym for diaspora. It is the only member of each of its synsets, 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 body of Jews (or Jewish communities) outside Palestine or modern Israel
the dispersion of the Jews outside Israel; from the destruction of the temple in Jerusalem in 587-86 BC when they were exiled to Babylonia up to the present time
the dispersion or spreading of something that was originally localized (as a people or language or culture)
Synonyms, antonyms and the broader and narrower relations for diaspora come from Princeton University’s WordNet. Full sources and licences.