WordNet records no synonym and no antonym for conditional sale. 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.
a security interest taken by the seller in return for credit
a sale in which the buyer receives title to the property only upon the performance of some condition (usually the full payment of the purchase price)
Synonyms, antonyms and the broader and narrower relations for conditional sale come from Princeton University’s WordNet. Full sources and licences.