fantasy has 5 distinct synonyms spread across 4 of its 4 senses. 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
fiction with a large amount of imagination in it
“she made a lot of money writing romantic fantasies”
Synonyms, antonyms and the broader and narrower relations for fantasy come from Princeton University’s WordNet. Full sources and licences.
something many people believe that is false
“they have the illusion that I am very wealthy”