quick has 13 distinct synonyms spread across 7 of its 8 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.
performed with little or no delay
“an immediate reply to my letter”
any area of the body that is highly sensitive to pain (as the flesh underneath the skin or a fingernail or toenail)
Synonyms, antonyms and the broader and narrower relations for quick come from Princeton University’s WordNet. Full sources and licences.