WordNet records no synonym and no antonym for aleatory contract. 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.
a contract whose performance by one party depends on the occurrence of an uncertain contingent event (but if it is contingent on the outcome of a wager it is not enforceable)
Synonyms, antonyms and the broader and narrower relations for aleatory contract come from Princeton University’s WordNet. Full sources and licences.