WordNet records no synonym and no antonym for cumulative vote. 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.
an election in which each person has as many votes as there are positions to be filled and they can all be cast for one candidate or can be distributed in any manner
Synonyms, antonyms and the broader and narrower relations for cumulative vote come from Princeton University’s WordNet. Full sources and licences.