WordNet records no synonym and no antonym for reinsurance. 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.
sharing the risk by insurance companies; part or all of the insurer's risk is assumed by other companies in return for part of the premium paid by the insured
“reinsurance enables a client to get coverage that would be too great for any one company to assume”
Synonyms, antonyms and the broader and narrower relations for reinsurance come from Princeton University’s WordNet. Full sources and licences.