quickness has 10 distinct synonyms spread across 3 of its 3 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.
skillful performance or ability without difficulty
“his quick adeptness was a product of good design”
intelligence as revealed by an ability to give correct responses without delay
a rate that is rapid
Synonyms, antonyms and the broader and narrower relations for quickness come from Princeton University’s WordNet. Full sources and licences.