diskette has 2 distinct synonyms spread across 1 of its 1 sense. 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.
a small plastic magnetic disk enclosed in a stiff envelope with a radial slit; used to store data or programs for a microcomputer
“floppy disks are noted for their relatively slow speed and small capacity and low price”
Synonyms, antonyms and the broader and narrower relations for diskette come from Princeton University’s WordNet. Full sources and licences.