prospective has no recorded synonym. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is retrospective.
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.
of or concerned with or related to the future
“prospective earnings”
Synonyms, antonyms and the broader and narrower relations for prospective come from Princeton University’s WordNet. Full sources and licences.