WordNet records no synonym and no antonym for pyramid scheme. 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 fraudulent scheme in which people are recruited to make payments to the person who recruited them while expecting to receive payments from the persons they recruit; when the number of new recruits fails to sustain the hierarchical payment structure the scheme collapses with most of the participants losing the money they put in
Synonyms, antonyms and the broader and narrower relations for pyramid scheme come from Princeton University’s WordNet. Full sources and licences.