WordNet records no synonym and no antonym for pump-and-dump 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.
an illegal scheme for making money by manipulating stock prices; the schemer persuades other people to buy the stock and then sells it himself as soon as the price of the stock rises
Synonyms, antonyms and the broader and narrower relations for pump-and-dump scheme come from Princeton University’s WordNet. Full sources and licences.